CDMA mobile communication system, base station, mobile station and communication control method during soft handover

ABSTRACT

In a CDMA mobile communication system comprising a plurality of base stations and a mobile station for making possible to communicate with said base stations by a soft handover, forward transmission between the mobile station and a particular base station is carried out when fading is small. When the fading is large, forward transmission between the mobile station and at least two base stations including the particular base station is carried out. The particular base station has a minimum propagation loss. When the fading is small, other base stations except for the particular base station turns the forward transmission off. Alternatively, the other base stations except for the particular base station lowers transmission power for the forward transmission when the fading is small.

This is a continuation of Application No. 09/372,053, filed Aug. 11,1999; now U.S. Pat. No. 6,526,028 the disclosure of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

This invention relates to a code division multiple access (CDMA) mobilecommunication system comprising a mobile station, a base station, a basestation control apparatus, and an exchange station and, in particular,to a forward transmission power control method in the CDMA mobilecommunication system.

In recent years, as a communication system for use in a mobilecommunication system, attention is directed to a time division multipleaccess (CDMA) communication system which is not affected by interferenceand interruption. The CDMA communication system is a communicationsystem in which a transmitting side spreads a user signal to betransmitted using a transmission spreading code to transmit a spreadsignal and a receiving side despreads the spread signal using areception spreading code identical with the transmission spreading codeto obtain an original user signal.

In addition, in the CDMA mobile communication system, a plurality oftransmitting sides carry out spreading operations using differenttransmission spreading codes having orthogonality, respectively, and thereceiving side can carry out identification of each communication byselecting, as the reception spreading code, one of the transmissionspreading codes to be used on carrying out despreading operation.Accordingly, it is possible to use the same frequency band in aplurality of communications.

However, it is difficult to perfectly maintain the orthogonality amongall of the spreading codes to be used. In actually, the respectivespreading codes are not perfectly orthogonal to one another and theneach spreading code has a correlation component with respect to otherspreading codes. As a result, the correlation component serves as aninterference component in its own communication and it results in adegradation factor in communication quality. Inasmuch as theinterference component occurs due to such a degradation factor, thelarger the number of communications becomes, the larger interferencecomponents becomes. As a result, it is possible to increase the numberof communication channels enable to multiplex in a frequency band ifeach communication channel has a low transmission power.

As a result, each base station in the CDMA mobile communication systemcarries out control of transmission power for each mobile station sothat each of received bit energy-to-interference ratios Eb/I0 (which areratios of desired received wave powers (Eb) to interference wave powers(I0)) obtained by communication channels established between the basestation and the respective mobile stations is equal to a necessary powerratio Eb/I0 required to insure the minimum communication quality. Thistransmission power control is called a reverse transmission powercontrol.

Specifically, a transmission power control (TPC) information signal forinstructing up/down of transmission power for the mobile station isincluded in a forward signal which is transmitted from the base stationto the mobile station via a forward link. By using the TRC informationsignal, the base station carries out an up instruction or a downinstruction of a current transmission power for each mobile station.

In the above-mentioned CDMA mobile communication system, each basestation covers a cell which is a area where the base station cancommunicate with the mobile station. In addition, the mobile stationmoves with a communication channel established between the mobilestation and a base station. When the mobile station goes out of the cellcovered by the base station, the mobile station must carry out ahandover for establishing a new communication channel with another basestation which cover a cell where the mobile station moves.

The mobile communication system adopting a spread spectrum systemcarries out a soft handover in order to maintain a service quality byavoiding a momentary interruption or the like on carrying out thehandover between the base stations. The soft handover is the handoverwhere the mobile station simultaneously carries out communication with aplurality of base stations and is a peculiar function to the spreadspectrum communication which can use the same radio frequency.

However, inasmuch as the same information signal is transmitted from theplurality of base stations to the mobile station when the soft handoveris carried out, transmission power in the forward link per communicationis much. As a result, interference power affecting other communicationsincreases and it results in a restriction of a communication capacity.

In order to improve such a restriction, for instance, a method ofdecreasing transmission power in the forward link per communication bycarrying out forward transmission from only one base station having aminimum propagation loss on the soft handover is disclosed in an articlecontributed by Furukawa (NEC Corporation) to the Communication SocietyConf., IEICE, B-5-118, March 1998.

However, it is impossible for this conventional forward transmissionpower control method to secure a user quality in a case where there is alarge fading in a communication channel. This is because the forwardtransmission is always carried out from only one base station on thesoft handover.

In a multimedia communication, prediction is made that a transmissionrate where a large capacity of data is transmitted from a data base at anetwork side to the mobile station is large. When the rate of themultimedia is large in future, it is necessary to increase a radiochannel capacity of the forward link in comparison with that of thereverse link. As a result, it is necessary to decrease the transmissionpower of the forward link.

In addition, as regards the reverse link which is a communicationchannel from the mobile station to the base station, one transmission isalways carried out per communication and an effect of the soft handoveris obtained by receiving in a plurality of base stations. Accordingly,the problem of increasing the transmission power does not arise oncarrying out the soft handover.

At any rate, the above-mentioned conventional CDMA mobile communicationsystem is disadvantageous in that the communication capacity of theforward link is restricted on carrying out the soft handover. This isbecause the transmission power of the forward link per communicationincreases and interference power affecting other communicationsincreases.

In addition, various other CDMA mobile communication systems related tothe present invention are already known. By way of example, JapaneseUnexamined Patent Publication of Tokkai No. Hei 8-172,390 or JP-A9-172390 discloses a mobile communication system which is capable ofreducing the influence of fading by selecting a plurality of basestations the reception powers from which at a mobile station exceed aprescribed value and simultaneously transmitting signals from these basestations to the mobile station with different frequencies and subjectingthem to diversity synthesis. According to JP-A 8-172390, transmittedfrom a mobile station, a signal is received by first and second basestations, and a control station performs diversity synthesis.Transmitted from the first and the second base stations, signals arereceived by the mobile station and are subjected to diversity synthesis.When the mobile station moves to a point in the vicinity of the boundaryof a first radio zone for the first base station and the reception powerfrom the first base station is reduced to the prescribed value orsmaller, communication with the first base station is switched to athird base station which the reception power from is larger. When themobile station moves a point in a second radio zone for the second basestation and the reception power from the second base station is reducedto the prescribed value or smaller, communication with the second basestation is switched to that with a fourth base station which thereception power from is larger. In the similar manner, communicationwith the third base station is switched to that with a fifth basestation at a point in the vicinity of the boundary of a third radio zonefor the third base station.

Japanese Unexamined Patent Publication of Tokkai No. Hei 6-13,956 orJP-A 6-013956 discloses a transmission power controller in a mobilecommunication and its system which are capable of increasing thecapacity of the system by implementing accurate transmission powercontrol at a mobile station side. According to JP-A 6-013956, a controlprocessor detects received power and the reception power is calculatedfrom a strength of a pilot signal fed from a searcher receiver in thiscase. Thus, the signal strength of a transmission signal from a basestation from which a mobile station is communicated is accuratelydetected. Furthermore, a fading speed is estimated from a change in thereceived power thereby controlling an averaging time in a transmissionpower controller. Thus, the system copes even with a change in thefading speed and the optimum averaging time is always obtained. Then anelectric field median strength is always detected without causing aresponse delay and accurate transmission power control is attained.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a CDMAmobile communication system which is capable of decreasing acommunication capacity in a forward link without degradation of aservice quality in a communication channel when a soft handover iscarried out.

Other objects of this invention will become clear as the descriptionproceeds.

According to an aspect of this invention, a method is for controllingcommunication in a code division multiple access (CDMA) mobilecommunication system comprising a plurality of base stations and amobile station for making possible to communicate with the base stationsby a soft handover. The method comprises the steps of carrying outforward transmission between the mobile station and a particular basestation when fading is small, and of carrying out forward transmissionbetween the mobile station and at least two base stations including theparticular base station when the fading is large.

According to an aspect of this invention, a method is for of controllingcommunication in a code division multiple access (CDMA) mobilecommunication system comprising a plurality of base stations and amobile station for making possible to communicate with the base stationsvia respective communication channels by a soft handover. The methodcomprises the steps of measuring, in the mobile station, propagationlosses in the communication channels to determine a particular basestation having a minimum propagation loss, of measuring, in the mobilestation, magnitude of fading in the communication channels to produce adetermined result indicative of whether or not the magnitude of thefading has a value which is larger than a predetermined threshold value,of transmitting, from the mobile station to the base stations via areverse link, as a forward transmission power information signal, acombination of a base station information signal indicative of theparticular base station, a fading information signal indicative of thedetermined result, and an error detection information signal forcarrying out error detection of the base station information signal andthe fading information signal, of decoding, in each of the basestations, the forward transmission power information signal to carry outthe error detection on the fading information signal and the basestation information signal using the error detection information signal,of turning, in each of the base stations, a forward transmission offwhen an error is not detected in the error detection, when the fadinginformation signal indicates that the value of the magnitude of thefading is smaller than the predetermined threshold value, and when itsown base station does not correspond to the particular base stationindicated by the base station information signal, and otherwise ofturning, in each of the base stations, the forward transmission on.

According to another aspect of this invention, a method is forcontrolling communication in a code division multiple access (CDMA)mobile communication system comprising a plurality of base stations anda mobile station for making possible to communicate with the basestations via respective communication channels by a soft handover. Themethod comprises the steps of measuring, in the mobile station,propagation losses in the communication channels to determine aparticular base station having a minimum propagation loss, oftransmitting, from the mobile station to the base stations via a reverselink, as a forward transmission power information signal, a combinationof a base station information signal indicative of the particular basestation and an error detection information signal for carrying out errordetection of the base station information signal, of decoding, in eachof tie base stations, the forward transmission power information signalto carry out the error detection on the base station information signalusing the error detection information signal, of determining, in each ofthe base stations, whether or not magnitude of fading on the reverselink has a value which is larger than a predetermined threshold value,of turning, in each of the base stations, a forward transmission offwhen an error is not detected in the error detection, when the value ofthe magnitude of the fading is smaller than the predetermined thresholdvalue, and when its own base station does not correspond to theparticular base station indicated by the base station informationsignal, and otherwise of turning, in each of the base stations, theforward transmission on.

According to sill another aspect of this invention, a method is forcontrolling communication in a code division multiple access (CDMA)mobile communication system comprising a plurality of base stations, abase station control apparatus connected to the base stations, and amobile station for making possible to communicate with the base stationsvia respective communication channels by a soft handover. The methodcomprises the steps of measuring, in the mobile station, magnitude offading in the communication channels to produce a determined resultindicative of whether or not the magnitude of the fading has a valuewhich is larger than a predetermined threshold value, of transmitting,from the mobile station to the base stations via a reverse link, as aforward transmission power information signal, a combination of a fadinginformation signal indicative of the determined result and an errordetection information signal for carrying out error detection of thefading information signal, of decoding, in each of the base stations,the forward transmission power information signal to carry out the errordetection on the fading information signal using the error detectioninformation signal, of comparing, in the base station control apparatus,bit energy-to-interference ratios of the base stations in the respectivecommunication channels to determine, as a particular base station, oneof the base stations that has a maximum bit energy-to-interferenceratio, of sending, from the base station control apparatus to the basestations, a base station information signal indicative of the particularbase station, of turning, in each of the base stations, a forwardtransmission off when an error is not detected in the error detection,when the fading information signal indicates that the value of themagnitude of the fading is smaller than the predetermined thresholdvalue, and when its own base station does not correspond to theparticular base station indicated by the base station informationsignal, and otherwise of turning, in each of the base stations, theforward transmission on.

According to yet another aspect of this invention, a method is forcontrolling communication in a code division multiple access (CDMA)mobile communication system comprising a plurality of base stations, abase station control apparatus connected to the base stations, and amobile station for making possible to communicate with the base stationsvia respective communication channels by a soft handover. The methodcomprising the steps of determining, in each of the base stations,whether or not magnitude of fading on a reverse link has a value whichis larger than a predetermined threshold value, of comparing, in thebase station control apparatus, bit energy-to-interference ratios of thebase stations in the respective communication channels to determine, asa particular base station, one of the base stations that has a maximumbit energy-to-interference ratio, of sending, from the base stationcontrol apparatus to the base stations, a base station informationsignal indicative of the particular base station, of turning, in each ofthe base stations, a forward transmission off when the value of themagnitude of the fading is smaller than the predetermined thresholdvalue and when its own base station does not correspond to theparticular base station indicated by the base station informationsignal, and otherwise of turning, in each of the base stations, theforward transmission on.

According to an aspect of this invention, a method is for controllingcommunication in a code division multiple access (CDMA) mobilecommunication system comprising a plurality of base stations and amobile station for making possible to communicate with the base stationsvia respective communication channels by a soft handover. The methodcomprises the steps of measuring, in the mobile station, propagationlosses in the communication channels to determine at least one specificbase station in which forward transmission should be turned on inaccordance with a predetermined reference value, of measuring, in themobile station, magnitude of fading in the communication channels toproduce a determined result indicative of whether or not the magnitudeof the fading has a value which is larger than a predetermined thresholdvalue, of transmitting, from the mobile station to the base stations viaa reverse link, as a forward transmission power information signal, acombination of a base station information signal indicative of the atleast one specific base station, a fading information signal indicativeof the determined result, and an error detection information signal forcarrying out error detection of the base station information signal andthe fading information signal, of decoding, in each of the basestations, the forward transmission power information signal to carry outthe error detection on the fading information signal and the basestation information signal using the error detection information signal,of turning, in each of the base stations, a forward transmission offwhen an error is not detected in the error detection, when the fadinginformation signal indicates that the value of the magnitude of thefading is smaller than the predetermined threshold value, and when itsown base station does not correspond to the at least one specific basestation indicated by the base station information signal, and otherwiseof turning, in each of the base stations, the forward transmission on.

According to another aspect of this invention, a method is forcontrolling communication in a code division multiple access (CDMA)mobile communication system comprising a plurality of base stations anda mobile station for making possible to communicate with the basestations via respective communication channels by a soft handover. Themethod comprises the steps of measuring, in the mobile station,propagation losses in the communication channels to determine at leastone specific base station in which forward transmission should be turnedon in accordance with a predetermined reference value, of transmitting,from the mobile station to the base stations via a reverse link, as aforward transmission power information signal, a combination of a basestation information signal indicative of the at least one specific basestation and an error detection information signal for carrying out errordetection of the base station information signal, of decoding, in eachof the base stations, the forward transmission power information signalto carry out the error detection on the base station information signalusing the error detection information signal, of determining, in each ofthe base stations, whether or not magnitude of fading on the reverselink has a value which is larger than a predetermined threshold value,of turning, in each of the base stations, a forward transmission offwhen an error is not detected in the error detection, when the value ofthe magnitude of the fading is smaller than the predetermined thresholdvalue, and when its own base station does not correspond to the at leastone specific base station indicated by the base station informationsignal, and otherwise of turning, in each of the base stations, theforward transmission on.

According to still another aspect of this invention, a method is forcontrolling communication in a code division multiple access (CDMA)mobile communication system comprising a plurality of base stations, abase station control apparatus connected to the base stations, and amobile station for making possible to communicate with the base stationsvia respective communication channels by a soft handover. The methodcomprises the steps of measuring, in the mobile station, magnitude offading in the communication channels to produce a determined resultindicative of whether or not the magnitude of the fading has a valuewhich is larger than a predetermined threshold value, of transmitting,from the mobile station to the base stations via a reverse link, as aforward transmission power information signal, a combination of a fadinginformation signal indicative of the determined result and an errordetection information signal for carrying out error detection of thefading information signal, of decoding, in each of the base stations,the forward transmission power information signal to carry out the errordetection on the fading information signal using the error detectioninformation signal, of comparing, in the base station control apparatus,bit energy-to-interference ratios of the base stations in the respectivecommunication channels to determine at least one specific base stationin which forward transmission should be turned on in accordance with apredetermined reference value, of sending, from the base station controlapparatus to the base stations, a base station information signalindicative of the at least one specific base station, of turning, ineach of the base stations, a forward transmission off when an error isnot detected in the error detection, when the fading information signalindicates that the value of the magnitude of the fading is smaller thanthe predetermined threshold value, and when its own base station doesnot correspond to the at least one specific base station indicated bythe base station information signal, and otherwise of turning, in eachof the base stations, the forward transmission on.

According to yet another aspect of this invention, a method is forcontrolling communication in a code division multiple access (CDMA)mobile communication system comprising a plurality of base stations, abase station control apparatus connected to the base stations, and amobile station for making possible to communicate with the base stationsvia respective communication channels by a soft handover. The methodcomprises the steps of determining, in each of the base stations,whether or not magnitude of fading on a reverse link has a value whichis larger than a predetermined threshold value, of comparing, in thebase station control apparatus, bit energy-to-interference ratios of thebase stations in the respective communication channels to determine atleast one specific base station in which forward transmission should beturned on in accordance with a predetermined reference value, ofsending, from the base station control apparatus to the base stations, abase station information signal indicative of the at least one specificbase station, of turning, in each of the base stations, a forwardtransmission off when the value of the magnitude of the fading issmaller than the predetermined threshold value and when its own basestation does not correspond to the at least one specific base stationindicated by the base station information signal, and otherwise ofturning, in each of the base stations, the forward transmission on.

According to an aspect of this invention, a method is for controllingcommunication in a code division multiple access (CDMA) mobilecommunication system comprising a plurality of base stations and amobile station for making possible to communicate with the base stationsvia respective communication channels by a soft handover. The methodcomprises the steps of measuring, in the mobile station, propagationlosses in the communication channels to determine a particular basestation having a minimum propagation loss, of measuring, in the mobilestation, magnitude of fading in the communication channels to produce adetermined result indicative of whether or not the magnitude of thefading has a value which is larger than a predetermined threshold value,of transmitting, from the mobile station to the base stations via areverse link, as a forward transmission power information signal, acombination of a base station information signal indicative of theparticular base station, a fading information signal indicative of thedetermined result, and an error detection information signal forcarrying out error detection of the base station information signal andthe fading information signal, of decoding, in each of the basestations, the forward transmission power information signal to carry outthe error detection on the fading information signal and the basestation information signal using the error detection information signal,of lowering, in each of the base stations, transmission power in aforward transmission from an original value when an error is notdetected in the error detection, when the fading information signalindicates that the value of the magnitude of the fading is smaller thanthe predetermined threshold value, and when its own base station doesnot correspond to the particular base station indicated by the basestation information signal, and otherwise of turning, in each of thebase stations, the transmission power of the forward transmission backto the original value.

According to another aspect of this invention, a method is forcontrolling communication in a code division multiple access (CDMA)mobile communication system comprising a plurality of base stations anda mobile station for making possible to communicate with the basestations via respective communication channels by a soft handover. Themethod comprises the steps of measuring, in the mobile station,propagation losses in the communication channels to determine aparticular base station having a minimum propagation loss, oftransmitting, from the mobile station to the base stations via a reverselink, as a forward transmission power information signal, a combinationof a base station information signal indicative of the particular basestation and an error detection information signal for carrying out errordetection of the base station information signal, of decoding, in eachof the base stations, the forward transmission power information signalto carry out the error detection on the base station information signalusing the error detection information signal, of determining, in each ofthe base stations, whether or not magnitude of fading on the reverselink has a value which is larger than a predetermined threshold value,of lowering, in each of the base stations, transmission power in aforward transmission from an original value when an error is notdetected in the error detection, when the value of the magnitude of thefading is smaller than the predetermined threshold value, and when itsown base station does not correspond to the particular base stationindicated by the base station information signal, and otherwise ofturning, in each of the base stations, the transmission power of theforward transmission back to the original value.

According to still another aspect of this invention, a method is forcontrolling communication in a code division multiple access (CDMA)mobile communication system comprising a plurality of base stations, abase station control apparatus connected to the base stations, and amobile station for making possible to communicate with the base stationsvia respective communication channels by a soft handover. The methodcomprises the steps of measuring, in the mobile station, magnitude offading in the communication channels to produce a determined resultindicative of whether or not the magnitude of the fading has a valuewhich is larger than a predetermined threshold value, of transmitting,from the mobile station to the base stations via a reverse link, as aforward transmission power information signal, a combination of a fadinginformation signal indicative of the determined result and an errordetection information signal for carrying out error detection of thefading information signal, of decoding, in each of the base stations,the forward transmission power information signal to carry out the errordetection on the fading information signal using the error detectioninformation signal, of comparing, in the base station control apparatus,bit energy-to-interference ratios of the base stations in the respectivecommunication channels to determine, as a particular base station, oneof the base stations that has a maximum bit energy-to-interferenceratio, of sending, from the base station control apparatus to the basestations, a base station information signal indicative of the particularbase station, of lowering, in each of the base stations, transmissionpower in a forward transmission from an original value when an error isnot detected in the error detection, when the fading information signalindicates that the value of the magnitude of the fading is smaller thanthe predetermined threshold value, and when its own base station doesnot correspond to the particular base station indicated by the basestation information signal, and otherwise of turning, in each of thebase stations, the transmission power of the forward transmission backto the original value.

According to yet another aspect of this invention, a method is forcontrolling communication in a code division multiple access (CDMA)mobile communication system comprising a plurality of base stations, abase station control apparatus connected to the base stations, and amobile station for making possible to communicate with the base stationsvia the respective communication channels by a soft handover. The methodcomprises the steps of determining, in each of the base stations,whether or not magnitude of fading on a reverse link has a value whichis larger than a predetermined threshold value, of comparing, in thebase station control apparatus, bit energy-to-interference ratios of thebase stations in the respective communication channels to determine, asa particular base station, one of the base stations that has a maximumbit energy-to-interference ratio, of sending, from the base stationcontrol apparatus to the base stations, a base station informationsignal indicative of the particular base station, of lowering, in eachof the base stations, transmission power in a forward transmission froman original value when the value of the magnitude of the fading issmaller than the predetermined threshold value and when its own basestation does not correspond to the particular base station indicated bythe base station information signal, and otherwise of turning, in eachof the base stations, the transmission power of the forward transmissionback to the original value.

According to an aspect of this invention, a method is for controllingcommunication in a code division multiple access (CDMA) mobilecommunication system comprising a plurality of base stations and amobile station for making possible to communicate with the base stationsvia respective communication channels by a soft handover. The methodcomprises the steps of measuring, in the mobile station, propagationlosses in the communication channels to determine at least one specificbase station in which forward transmission should be turned on inaccordance with a predetermined reference value, of measuring, in themobile station, magnitude of fading in the communication channels toproduce a determined result indicative of whether or not the magnitudeof the fading has a value which is larger than a predetermined thresholdvalue, of transmitting, from the mobile station to the base stations viaa reverse link, as a forward transmission power information signal, acombination of a base station information signal indicative of the atleast one specific base station, a fading information signal indicativeof the determined result, and an error detection information signal forcarrying out error detection of the base station information signal andthe fading information signal, of decoding, in each of the basestations, the forward transmission power information signal to carry outthe error detection on the fading information signal and the basestation information signal using the error detection information signal,of lowering, in each of the base stations, transmission power in aforward transmission from an original value when an error is notdetected in the error detection, when the fading information signalindicates that the value of the magnitude of the fading is smaller thanthe predetermined threshold value, and when its own base station doesnot correspond to the at least one specific base station indicated bythe base station information signal, and otherwise of turning, in eachof the base stations, the transmission power of the forward transmissionback to the original value.

According to another aspect of this invention, a method is forcontrolling communication in a code division multiple access (CDMA)mobile communication system comprising a plurality of base stations anda mobile station for making possible to communicate with the basestations via respective communication channels by a soft handover. Themethod comprises the steps of measuring, in the mobile station,propagation losses in the communication channels to determine at leastone specific base station in which forward transmission should be turnedon in accordance with a predetermined reference value, of transmitting,from the mobile station to the base stations via a reverse link, as aforward transmission power information signal, a combination of a basestation information signal indicative of the at least one specific basestation and an error detection information signal for carrying out errordetection of the base station information signal, of decoding, in eachof the base stations, the forward transmission power information signalto carry out the error detection on the base station information signalusing the error detection information signal, of determining, in each ofthe base stations, whether or not magnitude of fading on the reverselink has a value which is larger than a predetermined threshold value,of lowering, in each of the base stations, transmission power in aforward transmission from an original value when an error is notdetected in the error detection, when the value of the magnitude of thefading is smaller than the predetermined threshold value, and when itsown base station does not correspond to the at least one specific basestation indicated by the base station information signal, and otherwiseof turning, in each of said base stations, the transmission power of theforward transmission back to the original value.

According to still another aspect of this invention, a method is forcontrolling communication in a code division multiple access (CDMA)mobile communication system comprising a plurality of base stations, abase station control apparatus connected to the base stations, and amobile station for making possible to communicate with the base stationsvia respective communication channels by a soft handover. The methodcomprises the steps of measuring, in the mobile station, magnitude offading in the communication channels to produce a determined resultindicative of whether or not the magnitude of the fading has a valuewhich is larger than a predetermined threshold value, transmitting, fromthe mobile station to the base stations via a reverse link, as a forwardtransmission power information signal, a combination of a fadinginformation signal indicative of the determined result and an errordetection information signal for carrying out error detection of thefading information signal, of decoding, in each of the base stations,the forward transmission power information signal to carry out the errordetection on the fading information signal using the error detectioninformation signal, of comparing, in the base station control apparatus,bit energy-to-interference ratios of the base stations in the respectivecommunication channels to determine at least one specific base stationin which forward transmission should be turned on in accordance with apredetermined reference value, of sending, from the base station controlapparatus to the base stations, a base station information signalindicative of the at least one specific base station, of lowering, ineach of the base stations, transmission power in a forward transmissionfrom an original value when an error is not detected in the errordetection, when the fading information signal indicates that the valueof the magnitude of the fading is smaller than the predeterminedthreshold value, and when its own base station does not correspond tothe at least one specific base station indicated by the base stationinformation signal, and otherwise of turning, in each of the basestations, the transmission power of the forward transmission back to theoriginal value.

According to yet another aspect of this invention, a method is forcontrolling communication in a code division multiple access (CDMA)mobile communication system comprising a plurality of base stations, abase station control apparatus connected to the base stations, and amobile station for making possible to communicate with the base stationsvia respective communication channels by a soft handover. The methodcomprises the steps of determining, in each of the base stations,whether or not magnitude of fading on a reverse link has a value whichis larger than a predetermined threshold value, of comparing, in thebase station control apparatus, bit energy-to-interference ratios of thebase stations in the respective communication channels to determine atleast one specific base station in which forward transmission should beturned on in accordance with a predetermined reference value, ofsending, from the base station control apparatus to the base stations, abase station information signal indicative of the at least one specificbase station, of lowering, in each of the base stations, transmissionpower in a forward transmission from an original value when the value ofthe magnitude of the fading is smaller than the predetermined thresholdvalue and when its own base station does not correspond to the at leastone specific base station indicated by the base station informationsignal, and otherwise of turning, in each of the base stations, thetransmission power of the forward transmission back to the originalvalue.

According an aspect of this invention, a code division multiple access(CDMA) mobile communication system comprises first through N-th basestations and a mobile station for making possible to communicate withthe first through the N-th base stations via first through N-thcommunication channels by carrying out a soft handover, where Nrepresents a positive integer which is not less than two. The mobilestation comprises a propagation loss measuring arrangement for measuringfirst through N-th propagation losses in the first through the N-thcommunication channels to determine a particular base station having aminimum propagation loss and a fading measuring arrangement formeasuring magnitude of fading in the first through the N-thcommunication channels to produce a determined result indicative ofwhether of not the magnitude of the fading has a value which is largerthan a predetermined threshold value. Connected to the propagation lossmeasuring arrangement and the fading measuring arrangement, atransmitting arrangement transmits, to the first through the N-th basestations via a reverse link, as a forward transmission power informationsignal, a combination of a base station information signal indicative ofthe particular base station, a fading information signal indicative ofthe determined result, and an error detection information signal forcarrying out error detection of the base station information signal andthe fading information signal. An n-th base station, where n representseach of 1 through N, comprises a decoding arrangement for decoding theforward transmission power information signal to carry out the errordetection on the fading information signal and the base stationinformation signal using the error detection information signal.Connected to the decoding arrangement, a forward transmission on-offarrangement turns a forward transmission off when an error is notdetected in the error detection, when the fading information signalindicates that the value of the magnitude of the fading is smaller thanthe predetermined threshold value, and when the n-th base station doesnot correspond to said particular base station indicated by the basestation information signal. Otherwise, the forward transmission on-offarrangement turns the forward transmission on.

According to another aspect of this invention, a code division multipleaccess (CDMA) mobile communication system comprises first through N-thbase stations and a mobile station for making possible to communicatewith the first through the N-th base stations via first through N-thcommunication channels by carrying out a soft handover, where Nrepresents a positive integer which is not less than two. The mobilestation comprises a propagation loss measuring arrangement for measuringfirst through N-th propagation losses in the first through the N-thcommunication channels to determine a particular base station having aminimum propagation loss. Connected to the propagation loss measuringarrangement, a transmitting arrangement transmits, to the first throughthe N-th base stations via a reverse link, as a forward transmissionpower information signal, a combination of a base station informationsignal indicative of the particular base station and an error detectioninformation signal for carrying out error detection of the base stationinformation signal. An n-th base station, where n represents each of 1through N, comprises a decoding arrangement for decoding the forwardtransmission power information signal to carry out the error detectionon the base station information signal using the error detectioninformation signal and a fading determining arrangement for determiningwhether or not magnitude of fading on the reverse link has a value whichis larger than a predetermined threshold value. Connected to thedecoding arrangement and the fading determining arrangement, a forwardtransmission on-off arrangement turns a forward transmission off when anerror is not detected in the error detection, when the value of themagnitude of the fading is smaller than the predetermined thresholdvalue, and when said n-th base station does not correspond to theparticular base station indicated by the base station informationsignal. Otherwise, the forward transmission on-off arrangement turns theforward transmission on.

According to still another aspect of this invention, a code divisionmultiple access (CDMA) mobile communication system comprises firstthrough N-th base stations, a base station control apparatus connectedto the first through the N-th base stations, and a mobile station formaking possible to communicate with the first through the N-th basestations via first through N-th communication channels by carrying out asoft handover, where N represents a positive integer which is not lessthan two. The mobile station comprises a fading measuring arrangementfor measuring magnitude of fading in the first through the N-thcommunication channels to produce a determined result indicative ofwhether or not the magnitude of the fading has a value which is largerthan a predetermined threshold value. Connected to the fading measuringarrangement, a transmitting arrangement transmits, to the first throughthe N-th base stations via a reverse link, as a forward transmissionpower information signal, a combination of a fading information signalindicative of the determined result and an error detection informationsignal for carrying out error detection of the fading informationsignal. An n-th base station, where n represents each of 1 through N,comprises a decoding arrangement for decoding the forward transmissionpower information signal to carry out the error detection on the fadinginformation signal using the error detection information signal. Thebase station control apparatus comprises a comparing arrangement forcomparing first through N-th bit energy-to-interference ratios of thefirst through the N-th base stations in the first through the N-thcommunication channels to determine, as a particular base station, oneof the first through the N-th base stations that has a maximum bitenergy-to-interference ratio. Connected to the comparing means, asending means sends a base station information signal indicative of theparticular base station to the first through the N-th base stations. Then-th base station further comprises a forward transmission on-offarrangement, connected to the decoding arrangement and the sendingarrangement, for turning a forward transmission off when an error is notdetected in the error detection, when the fading information signalindicates that the value of the magnitude of the fading is smaller thanthe predetermined threshold value, and when the n-th base station doesnot correspond to the particular base station indicated by the basestation information signal. Otherwise, the forward transmission on-offarrangement turns the forward transmission on.

According to yet another aspect of this invention, a code divisionmultiple access (CDMA) mobile communication system comprises firstthrough N-th base stations, a base station control apparatus connectedto the first through the N-th base stations, and a mobile station formaking possible to communicate with the first through the N-th basestations via first through N-th communication channels by carrying out asoft handover, where N represents a positive integer which is not lessthan two. An n-th base station, where n represents each of 1 through N,comprises a fading determining arrangement for determining whether ornot magnitude of fading on a reverse link has a value which is largerthan a predetermined threshold value. The base station control apparatuscomprises a comparing arrangement for comparing first through N-th bitenergy-to-interference ratios of the first through the N-th basestations in said first through said N-th communication channels todetermine, as a particular base station, one of the first through saidN-th base stations that has a maximum bit energy-to-interference ratio.Connected to the comparing arrangement, a sending arrangement sends abase station information signal indicative of the particular basestation to the first through the N-th base stations. The n-th basestation further comprises a forward transmission on-off arrangement,connected to the fading determining arrangement and the sendingarrangement, for turning a forward transmission off when the value ofthe magnitude of the fading is smaller than the predetermined thresholdvalue and when the n-th base station does not correspond to theparticular base station indicated by the base station informationsignal. Otherwise, the forward transmission on-off arrangement turns theforward transmission on.

According to an aspect of this invention, a code division multipleaccess (CDMA) mobile communication system comprises first through N-thbase stations and a mobile station for making possible to communicatewith the first through the N-th base stations via first through N-thcommunication channels by carrying out a soft handover, where Nrepresents a positive integer which is not less than two. The mobilestation comprises a propagation loss measuring arrangement for measuringfirst through N-th propagation losses in the first through the N-thcommunication channels to determine at least one specific base stationin which forward transmission should be turned on in accordance with apredetermined reference value and a fading measuring arrangement formeasuring magnitude of fading in the first through the N-thcommunication channels to produce a determined result indicative ofwhether or hot the magnitude of the fading has a value which is largerthan a predetermined threshold value. Connected to the propagation lossmeasuring arrangement and the fading measuring arrangement, atransmitting arrangement transmits, to said base stations via a reverselink, as a forward transmission power information signal, a combinationof a base station information signal indicative of the at least onespecific base station, a fading information signal indicative of thedetermined result, and an error detection information signal forcarrying out error detection of the base station information signal andthe fading information signal. An n-th base station, where n representseach of 1 through N, comprises a decoding arrangement for decoding theforward transmission power information signal to carry out the errordetection on the fading information signal and the base stationinformation signal using the error detection information signal.Connected to the decoding arrangement, a forward transmission on-offarrangement turns a forward transmission off when an error is notdetected in the error detection, when the fading information signalindicates that the value of the magnitude of the fading is smaller thanthe predetermined threshold value, and when the n-th base station doesnot correspond to the at least one specific base station indicated bythe base station information signal. Otherwise, the forward transmissionon-off arrangement turns the forward transmission on.

According to another aspect of this invention, a code division multipleaccess (CDMA) mobile communication system comprises first through N-thbase stations and a mobile station for making possible to communicatewith the first through the N-th base stations via first through N-thcommunication channels by carrying out a soft handover, where Nrepresents a positive integer which is not less than two. The mobilestation comprises a propagation loss measuring arrangement for measuringfirst through N-th propagation losses in the first through the N-thcommunication channels to determine at least one specific base stationin which forward transmission should be turned on in accordance with apredetermined reference value. Connected to the propagation lossmeasuring arrangement, a transmitting arrangement transmit, to the basestations via a reverse link, as a forward transmission power informationsignal, a combination of a base station information signal indicative ofthe at least one specific base station and an error detectioninformation signal for carrying out error detection of the base stationinformation signal. An n-th base station, where n represents each of 1through N, comprises a decoding arrangement for decoding the forwardtransmission power information signal to carry out the error detectionon the base station information signal using the error detectioninformation signal and a fading determining arrangement for determiningwhether or not magnitude of fading on the reverse link has a value whichis larger than a predetermined threshold value. Connected to thedecoding arrangement and the fading determining arrangement, a forwardtransmission on-off arrangement turns a forward transmission off when anerror is not detected in the error detection, when the value of themagnitude of the fading is smaller than the predetermined thresholdvalue, and when the n-th base station does not correspond to the atleast one specific base station indicated by the base stationinformation signal. Otherwise, the forward transmission on-offarrangement turns the forward transmission on.

According to still another aspect of this invention, a code divisionmultiple access (CDMA) mobile communication system comprises firstthrough N-th base stations, a base station control apparatus connectedto the first through the N-th base stations, and a mobile station formaking possible to communicate with the first through the N-th basestations via first through N-th communication channels by carrying out asoft handover, where N represents a positive integer which is not lessthan two. The mobile station comprises a fading measuring arrangementfor measuring magnitude of fading in the first through the N-thcommunication channels to produce a determined result indicative ofwhether or not the magnitude of the fading has a value which is largerthan a predetermined threshold value. Connected to the fading measuringarrangement, a transmitting arrangement transmits, to the first throughthe N-th base stations via a reverse link, as a forward transmissionpower information signal, a combination of a fading information signalindicative of the determined result and an error detection informationsignal for carrying out error detection of the fading informationsignal. An n-th base station, where n represents each of 1 through N,comprises a decoding arrangement for decoding the forward transmissionpower information signal to carry out the error detection on the fadinginformation signal using the error detection information signal. Thebase station control apparatus comprises a comparing arrangement forcomparing first through N-th bit energy-to-interference ratios of thefirst through the N-th base stations in the first through the N-thcommunication channels to determine at least one specific base stationin which forward transmission should be turned on in accordance with apredetermined reference value. Connected to the comparing arrangement, asending arrangement sends a base station information signal indicativeof the at least one specific base station to the first through the N-thbase stations. The n-th base station further comprises a forwardtransmission on-off arrangement, connected to the decoding arrangementand the sending arrangement, for turning a forward transmission off whenan error is not detected in the error detection, when the fadinginformation signal indicates that the value of the magnitude of thefading is smaller than the predetermined threshold value, and when then-th base station does not correspond to the least one specific basestation indicated by the base station information signal. Otherwise, theforward transmission on-off arrangement turns the forward transmissionon.

According to yet another aspect of this invention, a code divisionmultiple access (CDMA) mobile communication system comprises firstthrough N-th base stations, a base station control apparatus connectedto the first through the N-th base stations, and a mobile station formaking possible to communicate with the first through the N-th basestations via first through N-th communication channels by carrying out asoft handover, where N represents a positive integer which is not lessthan two. An n-th base station, where n represents each of 1 through N,comprises a fading determining arrangement for determining whether ornot magnitude of fading on a reverse link has a value which is largerthan a predetermined threshold value. The base station control apparatuscomprises a comparing arrangement for comparing first through N-th bitenergy-to-interference ratios of the first through the N-th basestations in the first through the N-th communication channels todetermine at least one specific base station in which forwardtransmission should be turned on in accordance with a predeterminedreference value. Connected to the comparing arrangement, a sendingarrangement sends a base station information signal indicative of the atleast one specific base station to the first through the N-th basestations. The n-th base station further comprises a forward transmissionon-off arrangement, connected to the fading determining arrangement andthe sending arrangement, for turning a forward transmission off when thevalue of the magnitude of the fading is smaller than the predeterminedthreshold value and when the n-th base station does not correspond tosaid at least one specific base station indicated by the base stationinformation signal. Otherwise, the forward transmission on-offarrangement turns the forward transmission on.

According to an aspect of this invention, a code division multipleaccess (CDMA) mobile communication system comprises first through N-thbase stations and a mobile station for making possible to communicatewith the first through the N-th base stations via first through N-thcommunication channels by carrying out a soft handover, where Nrepresents a positive integer which is not less than two. The mobilestation comprises a propagation loss measuring arrangement for measuringfirst through N-th propagation losses in the first through the N-thcommunication channels to determine a particular base station having aminimum propagation loss and a fading measuring arrangement formeasuring magnitude of fading in the first through the N-thcommunication channels to produce a determined result indicative ofwhether or not the magnitude of the fading has a value which is largerthan a predetermined threshold value. Connected to the propagation lossmeasuring arrangement and the fading measuring arrangement, atransmitting arrangement transmits, to the first through the N-th basestations via a reverse link, as a forward transmission power informationsignal, a combination of a base station information signal indicative ofthe particular base station, a fading information signal indicative ofthe determined result, and an error detection information signal forcarrying out error detection of the base station information signal andthe fading information signal. An n-th base station, where n representseach of 1 through N, comprises a decoding arrangement for decoding theforward transmission power information signal to carry out the errordetection on the fading information signal and the base stationinformation signal using the error detection information signal.Connected to the decoding arrangement, a transmission power controllingarrangement lowers transmission power in a forward transmission from anoriginal value when an error is not detected in the error detection,when the fading information signal indicates that the value of themagnitude of the fading is smaller than the predetermined thresholdvalue, and when the n-th base station does not correspond to theparticular base station indicated by the base station informationsignal. Otherwise, the transmission power controlling arrangement turnsthe transmission power of the forward transmission back to the originalvalue.

According to another aspect of this invention, a code division multipleaccess (CDMA) mobile communication system comprises first through N-thbase stations and a mobile station for making possible to communicatewith the first through the N-th base stations via first through N-thcommunication channels by carrying out a soft handover, where Nrepresents a positive integer which is not less than two. The mobilestation comprises a propagation loss measuring arrangement for measuringfirst through N-th propagation losses in the first through the N-thcommunication channels to determine a particular base station having aminimum propagation loss. Connected to the propagation loss measuringarrangement, a transmitting arrangement transmits, to the first throughthe N-th base stations via a reverse link, as a forward transmissionpower information signal, a combination of a base station informationsignal indicative of the particular base station and an error detectioninformation signal for carrying out error detection of the base stationinformation signal. An n-th base station, where n represents each of 1through N, comprises a decoding arrangement for decoding the forwardtransmission power information signal to carry out the error detectionon the base station information signal using the error detectioninformation signal and a fading determining arrangement for determiningwhether or not magnitude of fading on the reverse link has a value whichis larger than a predetermined threshold value. Connected to thedecoding arrangement and the fading determining arrangement, atransmission power controlling arrangement lowers transmission power ina forward transmission from an original value when an error is notdetected in the error detection, when the value of the magnitude of thefading is smaller than the predetermined threshold value, and when then-th base station does not correspond to said particular base stationindicated by the base station information signal. Otherwise, thetransmission power controlling arrangement turns the transmission powerof the forward transmission back to the original value.

According to still another aspect of this invention, a code divisionmultiple access (CDMA) mobile communication system comprises firstthrough N-th base stations, a base station control apparatus connectedto the first through the N-th base stations, and a mobile station formaking possible to communicate with the first through the N-th basestations via first through N-th communication channels by carrying out asoft handover, where N represents a positive integer which is not lessthan two. The mobile station comprises a fading measuring arrangementfor measuring magnitude of fading in the first through the N-thcommunication channels to produce a determined result indicative ofwhether or not the magnitude of the fading has a value which is largerthan a predetermined threshold value. Connected to the fading measuringarrangement, a transmitting arrangement transmits, to the first throughthe N-th base stations via a reverse link, as a forward transmissionpower information signal, a combination of a fading information signalindicative of the determined result and an error detection informationsignal for carrying out error detection of the fading informationsignal. An n-th base station, where n represents each of 1 through N,comprises a decoding arrangement for decoding the forward transmissionpower information signal to carry out the error detection on the fadinginformation signal using the error detection information signal. Thebase station control apparatus comprises a comparing arrangement forcomparing first through N-th bit energy-to-interference ratios of thefirst through the N-th base stations in said first through the N-thcommunication channels to determine, as a particular base station, oneof the base stations that has a maximum bit energy-to-interferenceratio. Connected to the comparing arrangement, a sending arrangementsends a base station information signal indicative of the particularbase station to the first through the N-th base stations. The n-th basestation further comprises a transmission power controlling arrangementfor lowering transmission power in a forward transmission from anoriginal value when an error is not detected in the error detection,when the fading information signal indicates that the value of themagnitude of the fading is smaller than the predetermined thresholdvalue, and when said n-th base station does not correspond to theparticular base station indicated by the base station informationsignal. Otherwise, the transmission power controlling arrangement turnsthe transmission power of the forward transmission back to the originalvalue.

According to yet another aspect of this invention, a code divisionmultiple access (CDMA) mobile communication system comprises firstthrough N-th base stations, a base station control apparatus connectedto the first through the N-th base stations, and a mobile station formaking possible to communicate with the first through the N-th basestations via first through N-th communication channels by carrying out asoft handover, where N represents a positive integer which is not lessthan two. An n-th base station, where n represents each of 1 through N,comprises a fading determining arrangement for determining whether ornot magnitude of fading on a reverse link has a value which is largerthan a predetermined threshold value. The base station control apparatuscomprises a comparing arrangement for comparing first through N-th bitenergy-to-interference ratios of the first through the N-th basestations in the first through the N-th communication channels todetermine, as a particular base station, one of the first though theN-th base stations that has a maximum bit energy-to-interference ratio.Connected to the comparing means, a sending arrangement sends a basestation information signal indicative of the particular base station tothe first through the N-th base stations. The n-th base station furthercomprises a transmission power controlling arrangement, connected to thefading determining arrangement and the sending arrangement, for loweringtransmission power in a forward transmission from an original value whenthe value of the magnitude of the fading is smaller than thepredetermined threshold value and when the n-th base station does notcorrespond to the particular base station indicated by the base stationinformation signal. Otherwise, the transmission power controllingarrangement turns the transmission power of the forward transmissionback to the original value.

According to an aspect of this invention, a code division multipleaccess (CDMA),mobile communication system comprises first through N-thbase stations and a mobile station for making possible to communicatewith the first through the N-th base stations via first through N-thcommunication channels by carrying out a soft handover, where Nrepresents a positive integer which is not less than two. The mobilestation comprises a propagation loss measuring arrangement for measuringfirst through N-th propagation losses in the first through the N-thcommunication channels to determine at least one specific base stationin which forward transmission should be turned on in accordance with apredetermined reference value and a fading measuring arrangement formeasuring magnitude of fading in the first through the N-thcommunication channels to produce a determined result indicative ofwhether or not the magnitude of the fading has a value which is largerthan a predetermined threshold value. Connected to the propagation lossmeasuring arrangement and the fading measuring arrangement, atransmitting arrangement transmits, to the first through the N-th basestations via a reverse link, as a forward transmission power informationsignal, a combination of a base station information signal indicative ofthe at least one specific base station, a fading information signalindicative of the determined result, and an error detection informationsignal for carrying out error detection of the base station informationsignal and the fading information signal. An n-th base station, whereinn represents each of 1 through N, comprises a decoding arrangement fordecoding the forward transmission power information signal to carry outthe error detection on the fading information signal and the basestation information signal using the error detection information signal.Connected to the decoding arrangement, a transmission power controllingarrangement lowers transmission power in a forward transmission from anoriginal value when an error is not detected in the error detection,when the fading information signal indicates that the value of themagnitude of the fading is smaller than the predetermined thresholdvalue, and when the n-th base station does not correspond to said atleast one specific base station indicated by the base stationinformation signal. Otherwise, the transmission power controllingarrangement turns the transmission power of the forward transmissionback to the original value.

According to another aspect of this invention, a code division multipleaccess (CDMA) mobile communication system comprises first through N-thbase stations and a mobile station for making possible to communicatewith the first through the N-th base stations via first through N-thcommunication channels by carrying out a soft handover, where Nrepresents a positive integer which is not less than two. The mobilestation comprises a propagation loss measuring arrangement for measuringfirst through N-th propagation losses in the first through N-thcommunication channels to determine at least one specific base stationin which forward transmission should be turned on in accordance with apredetermined reference value. Connected to the propagation lossmeasuring arrangement, a transmitting arrangement transmits, to thefirst through the N-th base stations via a reverse link, as a forwardtransmission power information signal, a combination of a base stationinformation signal indicative of the at least one specific base stationand an error detection information signal for carrying out errordetection of the base station information signal. An n-th base station,where n represents each of 1 through N, comprises a decoding arrangementfor decoding the forward transmission power information signal to carryout the error detection on the base station information signal using theerror detection information signal and a fading determining arrangementfor determining whether or not magnitude of fading on the reverse linkhas a value which is larger than a predetermined threshold value.Connected to the decoding arrangement and the fading determiningarrangement, a transmission power controlling arrangement lowerstransmission power in a forward transmission from an original value whenan error is not detected in the error detection, when the value of themagnitude of the fading is smaller than the predetermined thresholdvalue, and when the n-th base station does not correspond to the atleast one specific base station indicated by the base stationinformation signal. Otherwise, the transmission power controllingarrangement turns the transmission power of the forward transmissionback to the original value.

According to still another aspect of this invention, a code divisionmultiple access (CDMA) mobile communication system comprises firstthrough N-th base stations, a base station control apparatus connectedto the first through the N-th base stations, and a mobile station formaking possible to communicate with the first through the N-th basestations via first through N-th communication channels by carrying out asoft handover, where N represents a positive integer which is not lessthan two. The mobile station comprises a fading measuring arrangementfor measuring magnitude of fading in the first through the N-thcommunication channels to produce a determined result indicative ofwhether or not the magnitude of the fading has a value which is largerthan a predetermined threshold value. Connected to the fading measuringarrangement, a transmitting arrangement transmits, to the first throughthe N-th base stations via a reverse link, as a forward transmissionpower information signal, a combination of a fading information signalindicative of the determined result and an error detection informationsignal for carrying out error detection of the fading informationsignal. An n-th base station, where n represents each of 1 through N,comprises a decoding arrangement for decoding the forward transmissionpower information signal to carry out the error detection on the fadinginformation signal using the error detection information signal. Thebase station control apparatus comprises a comparing arrangement forcomparing first through N-th bit energy-to-interference ratios of thefirst through the N-th base stations in the first through the N-thcommunication channels to determine at least one specific base stationin which forward transmission should be turned on in accordance with apredetermined reference value. Connected to the comparing arrangement, asending arrangement sends a base station information signal indicativeof said at least one specific base station to the first through the N-thbase stations. The n-th base station further comprises a transmissionpower controlling arrangement, connected to the decoding arrangement andthe sending arrangement, for lowering transmission power in a forwardtransmission from an original value when an error is not detected in theerror detection, when the fading information signal indicates that thevalue of the magnitude of the fading is smaller than the predeterminedthreshold value, and when the n-th base station does not correspond tosaid at least one specific base station indicated by the base stationinformation signal. Otherwise, the transmission power controllingarrangement turns the transmission power of the forward transmissionback to the original value.

According to yet another aspect of this invention, a code divisionmultiple access (CDMA) mobile communication system comprises firstthrough N-th base stations, a base station control apparatus connectedto the first through the N-th base stations, and a mobile station formaking possible to communicate with the first through the N-th basestations via first through N-th communication channels by carrying out asoft handover, where N represents a positive integer which is not lessthan two. An n-th base station, where n represents each of 1 through N,comprises a fading determining arrangement for determining whether ornot magnitude of fading on a reverse link has a value which is largerthan a predetermined threshold value. The base station control apparatuscomprises a comparing arrangement for comparing first through N-th bitenergy-to-interference ratios of the first through the N-th basestations in the first through the N-th communication channels todetermine at least one specific base station in which forwardtransmission should be turned on in accordance with a predeterminedreference value. Connected to the comparing arrangement, a sendingarrangement sends a base station information signal indicative of the atleast one specific base station to the first through the N-th basestations. The n-th base station further comprises a transmission powercontrolling arrangement, connected to the fading determining arrangementand the sending arrangement, for lowering transmission power in aforward transmission from an original value when the value of themagnitude of the fading is smaller than the predetermined thresholdvalue and when the n-th base station does not correspond to the at leastone specific base station indicated by the base station informationsignal. Otherwise, the transmission power controlling arrangement turnsthe transmission power of the forward transmission back to the originalvalue.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a block diagram of a conventional CDMA mobile communicationsystem;

FIG. 2 is a block diagram of a conventional mobile station for use inthe CDMA mobile communication system illustrated in FIG. 1;

FIG. 3 is a block diagram of a conventional base station for use in theCDMA mobile communication system illustrated in FIG. 1;

FIG. 4 is a view showing a case where two base stations carry outforward transmission to one mobile station;

FIG. 5 is a view showing another case where one base station carries outforward transmission to one mobile station;

FIG. 6 is a flow chart for use in describing operation of the CDMAmobile communication system illustrated in FIG. 1;

FIG. 7 is a block diagram of a CDMA mobile communication systemaccording to a first embodiment of this invention;

FIG. 8 is a block diagram of a mobile station for use in the CDMA mobilecommunication system illustrated in FIG. 7;

FIG. 9 is a block diagram of a base station for use in the CDMA mobilecommunication system illustrated in FIG. 7;

FIG. 10 is a flow chart for use in describing operation of the mobilestation illustrated in FIG. 8;

FIGS. 11A through 11C collectively show variations of a received levelaccording to a transmission power control in a case where fading islarge;

FIGS. 12A through 12C collectively show variations of a received levelaccording to a transmission power control in a case where fading issmall;

FIG. 13 is a view for use in describing a moving average;

FIG. 14 is a view for use in describing a method of calculating anaverage value to using an oblivion coefficient;

FIGS. 15A and 15B show formats of a forward link and a reverse like,respectively;

FIG. 16 is a flow chart for use in describing operation of the basestation illustrated in FIG. 9;

FIG. 17 is a block diagram of a CDMA mobile communication systemaccording to a second embodiment of this invention;

FIG. 18 is a block diagram of a mobile station for use in the CDMAmobile communication system illustrated in FIG. 17;

FIG. 19 is a block diagram of a base station for use in the CDMA mobilecommunication system illustrated in FIG. 17;

FIG. 20 is a flow chart for use in describing operation of the mobilestation illustrated in FIG. 18;

FIG. 21 is a flow chart for use in describing operation of the basestation illustrated in FIG. 19;

FIG. 22 is a block diagram of a CDMA mobile communication systemaccording to a third embodiment of this invention;

FIG. 23 is a block diagram of a mobile station for use in the CDMAmobile communication system illustrated in FIG. 22;

FIG. 24 is a block diagram of a base station for use in the CDMA mobilecommunication system illustrated in FIG. 22;

FIG. 25 is a flow chart for use in describing operation of the mobilestation illustrated in FIG. 23;

FIG. 26 is a flow chart for use in describing operation of the basestation illustrated in FIG. 24;

FIG. 27 is a block diagram of a CDMA mobile communication systemaccording to a forth embodiment of this invention;

FIG. 28 is a block diagram of a base station for use in the CDMA mobilecommunication system illustrated in FIG. 27;

FIG. 29 is a flow chart for use in describing operation of the basestation illustrated in FIG. 28;

FIG. 30 is a table showing differences among the first through thefourth embodiments of this invention; and

FIG. 31 is a view for use in describing a sectorized CDMA mobilecommunication system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a conventional code division multiple access (CDMA)mobile communication system will be described in order to facilitate anunderstanding of the present invention. The illustrated CDMA mobilecommunication system comprises a mobile station 10′, first and secondbase stations 20′₁ and 20′₂ which communicate with the mobile station10′, a base station control apparatus 30 connected to the first and thesecond base stations 20′₁ and 20′₂, and an exchange station 40 connectedto the base station control apparatus 30. The first and the second basestations 20′₁ and 20′₂ are similar in structure and operation eachother.

Practically, the exchange station 40 is connected to other base stationcontrol apparatuses in addition to the base station control apparatus30. In addition, the base station control apparatus 30 is connected toother base stations in addition to the first and the second basestations 20′₁ and 20′₂. Furthermore, each of the first and the secondbase stations 20′₁ and 20′₂ communicates with other mobile stations inaddition to the mobile station 10′. The other base station controlapparatuses, the other base stations, and the other mobile stations areherein omitted from FIG. 1 because of simplification of description.

In addition, the base station control apparatus 30 comprises anasynchronous transfer mode (ATM) switch 31 and a control section 32. TheATM switch 31 receives an ATM cell from the exchange station 40 andtransmits the ATM cell as user information signals 51 to the first andthe second base stations 20′₁ and 20′₂ in accordance with destinationaddresses. The control section 32 transmits, to the first and the secondbase stations 20′₁ and 20′₂, control information signals 52 forcontrolling operations of the first and the second base stations 20′₁and 20′₂.

Turning to FIG. 2, the description will proceed to a conventional mobilestation 10′ for use in the CDMA mobile communication system illustratedin FIG. 1. The mobile station 10′ comprises a mobile demodulator 101, amobile analog-to-digital converter 102, a mobile communication channelRake receiver 103, a mobile decoding section 104, first through thirdperch channel Rake receivers 105 ₁, 105 ₂, and 105 ₃, first throughthird perch channel reception level measuring sections 106 ₁, 106 ₂, and106 ₃, a mobile control section 107′, a mobile reception level measuringsection 108, a mobile subtracter 109, a mobile transmission powercalculating section 111, a mobile encoding section 112, a mobiledigital-to-analog converter 113, a mobile modulator 114, and firstthrough third perch channel decoding sections 115 ₁, 115 ₂, and 115 ₃.

In the mobile station 10′, a received forward signal is supplied to themobile demodulator 101. The mobile demodulator 101 demodulates thereceived forward signal into a mobile baseband signal. The mobilebaseband signal is supplied to the mobile analog-to-digital converter102. The mobile analog-to-digital converter 102 converts the mobilebaseband signal into a mobile digital signal. The mobile digital signalis supplied to the mobile communication channel Rake receiver 103 andthe first through the third perch channel RAKE receivers 105 ₁ to 105 ₃.The mobile communication channel RAKE receiver 103 carries out Rakesynthesization on the mobile digital signal to produce a mobilesynthesized signal. The mobile synthesized signal is supplied to themobile decoding section 104 and the mobile reception level measuringsection 108. The mobile decoding section 104 decodes the mobilesynthesized signal to extract a mobile received user information signal.The mobile reception level measuring section 108 measures a mobilecommunication channel reception level of the mobile synthesized signalto produce a mobile communication channel reception level signalindicative of the mobile communication channel reception level. Themobile communication channel reception level signal is supplied to themobile subtracter 109 and the mobile control section 107′.

Each base station is assigned with a perch channel. Each base stationbroadcasts a base station information signal via the perch channel. Eachmobile station under each base station receives the base stationinformation signal via the perch channel. The base station informationsignal is a part of a radio resource (RR) information signal which isexchanged between the mobile control section 107′ in the mobile station10′ and the base control section 207′ in the base station 20′. Inaddition, the base station information signal includes a transmissionpower value.

Supplied with the mobile digital signal, the first through the thirdperch channel RAKE receivers 105 ₁ to 105 ₃ receive first through thirdperch signals in the mobile digital signal on first through third perchchannels, respectively. The first through the third perch signals aresupplied to the first through the third perch channel reception levelmeasuring sections 106 ₁ to 106 ₃, respectively. The first through thethird perch channel reception level measuring sections 106 ₁ to 106 ₃measure first through third perch channel reception levels of the firstthrough the third perch signals to produce first through third perchchannel reception level signals indicative of the first through thethird perch channel reception levels, respectively. The first throughthe third perch channel reception level signals are sent to the mobilecontrol section 107′.

In addition, the first through the third perch signals are supplied tothe first through the third channel decoding sections 115 ₁ to 115 ₃,respectively. More specifically, the base station information signal isreceived in each of the first through the third perch channel RAKEreceivers 105 ₁ to 105 ₃ through the mobile demodulator 101 and theanalog-to-digital converter 102. Thereafter, the base stationinformation signal is sent from the first through the third perchchannel RAKE receivers 105 ₁ to 105 ₃ to the first through the thirdchannel decoding sections 115 ₁ to 115 ₃. Each of the first through thethird perch channel decoding sections 115 ₁ to 115 ₃ decodes the basestation information signal to extract the transmission power value fromthe base station information signal. The transmission power value issupplied from each of the first through the third perch channel decodingsection 115 ₁ to 115 ₃ to the mobile control section 107′.

The control mobile section 107′ supplies a mobile target level signalindicative of a mobile target level to the mobile subtracter 109.Supplied with the mobile communication channel reception level signaland the mobile target level signal, the mobile subtracter 109 subtractsthe mobile target level indicated by the mobile target level signal fromthe mobile communication channel reception level indicated by the mobilecommunication channel reception level signal to produce a mobilesubtracted signal indicative of a difference between the mobilecommunication channel reception level and the mobile target level. Themobile subtracted signal is supplied to the mobile transmission powercalculating section 111. The mobile transmission power calculatingsection 111 calculates a forward transmission power on the basis of themobile subtracted signal to produce a forward transmission powerinformation signal indicative of the forward transmission power. Theforward transmission power information signal is supplied to the mobiledigital-to-analog converter 113.

The mobile encoding section 112 is supplied with a mobile transmissionuser information signal. The mobile encoding section 112 encodes themobile transmission user information signal into a mobile encodedsignal. The mobile encoded signal is supplied to the mobiledigital-to-analog converter 113. The mobile digital-to-analog converter113 converts the mobile encoded signal with the mobile forwardtransmission power information signal into a mobile analog signal. Themobile analog signal is supplied to the mobile modulator 114. The mobilemodulator 114 modulates a carrier signal by the mobile analog signal toproduce a mobile modulated signal. The mobile modulated signal istransmitted as a reverse transmission signal to the base station via areverse link.

Turning to FIG. 3, the description will proceed to a conventional basestation 20′ (suffix omitted) for use in the CDMA mobile communicationsystem illustrated in FIG. 1. The base station 20′ comprises a basedemodulator 201, a base analog-to-digital converter 202, a basecommunication channel Rake receiver 203, a base decoding section 204, abase control section 207′, a base reception level measuring section 208,a base subtracter 209, a base transmission power calculating section211, a base encoding section 212, a base digital-to-analog converter213, and a base modulator 214.

In the base station 20′, a received reverse signal is supplied to thebase demodulator 201. The base demodulator 201 demodulates the receivedreverse signal into a base baseband signal. The base baseband signal issupplied to the base analog-to-digital converter 202. The baseanalog-to-digital converter 202 converts the base baseband signal into abase digital signal. The base digital signal is supplied to the basecommunication channel Rake receiver 203. The base communication channelRake receiver 203 carries out Rake synthesization on the base digitalsignal to produce a base synthesized signal. The base synthesized signalis supplied to the base decoding section 204 and the base receptionlevel measuring section 208. The base decoding section 204 decodes thebase synthesized signal to extract a base received user informationsignal. The base reception level measuring section 208 measures a basecommunication channel reception level of the base synthesized signal toproduce a base communication channel reception level signal indicativeof the base communication channel reception level. The basecommunication channel reception level signal is supplied to the basesubtracter 209.

The base control section 207′ supplies a base target level signalindicative of a base target level to the base subtracter 209. The basecontrol section 207 supplies a forward transmission on/off instructionsignal to the base transmission power calculating section 211.

Supplied with the base communication channel reception level signal andthe base target level signal, the base subtracter 209 subtracts the basetarget level indicated by the base target level signal from the basecommunication channel reception level indicated by the basecommunication channel reception level signal to produce a basesubtracted signal indicative of a difference between the basecommunication channel reception level and the base target level. Thebase subtracted signal is supplied to the base transmission powercalculating section 211. The base transmission power calculating section111 calculates a forward transmission power on the basis of the basesubtracted signal and the forward transmission on/off instruction signalto produce a forward transmission power information signal indicative ofthe forward transmission power. The forward transmission powerinformation signal is supplied to the base digital-to-analog converter213.

The base encoding section 212 is supplied with a base transmission userinformation signal. The base encoding section 212 encodes the basetransmission user information signal into a base encoded signal. Thebase encoded signal is supplied to the base digital-to-analog converter213. The base digital-to-analog converter 213 converts the base encodedsignal on the bases of the forward transmission power information signalinto a base analog signal. The base analog signal is supplied to thebase modulator 214. The base modulator 214 modulates a carrier signal bythe base analog signal to produce a base modulated signal. The basemodulated signal is transmitted as a forward transmission signal to themobile station via a forward link.

In the above-mentioned CDMA mobile communication system, each basestation covers a cell which is a area where the base station cancommunicate with the mobile station. In addition, the mobile stationmoves with a communication channel established between the mobilestation and a base station. When the mobile station goes out of the cellcovered by the base station, the mobile station must carry out ahandover for establishing a new communication channel with another basestation which cover a cell where the mobile station moves.

The mobile communication system adopting a spread spectrum systemcarries out a soft handover in order to maintain a service quality byavoiding a momentary interruption or the like on carrying out thehandover between the base stations. As shown in FIG. 4, the softhandover is the handover where the mobile station 10′ simultaneouslycarries out communication with a plurality of base stations 20′₁ and20′₂ and is a peculiar function to the spread spectrum communicationwhich can use the same radio frequency.

However, inasmuch as the same information signal is transmitted from theplurality of base stations 20′₁ and 20′₁ to the mobile station 10′ whenthe soft handover is carried out, transmission power in the forward linkper communication is much. As a result, interference power affectingother communications increases and it results in a restriction of acommunication capacity.

In order to improve such a restriction, for instance, a method ofdecreasing transmission power in the forward link per communication bycarrying out forward transmission from one base station having the leastpropagation loss on the soft handover, as illustrated in FIG. 5, isdisclosed in an article contributed by Furukawa (NEC Corporation) to theCommunications Society Conf., IEICE, B-5-118, March 1998.

Referring to FIG. 6 in addition to FIG. 5, the description will proceedto the method of decreasing the transmission power in the forward link.

At a step S101′, the mobile station 10′ calculates propagation lossesfor communication channels between the mobile station 10′ and the firstand the second base stations 20′₁ and 20′₂ around the mobile station10′. The step S101′ is followed by a step S102′ at which the mobilestation 10′ sends propagation loss signals indicative of the propagationlosses to the base station control apparatus 30 through the first andthe second base stations 20′₁ and 20′₂. The step S102′ proceeds to astep S103′ at which the base station control apparatus 30 determines aspecific base station having the propagation loss which is less than apredetermined threshold value.

In the example being illustrated, the specific base station is the firstbase station 20′₁. In other words, the second base station 20′₂ has thepropagation loss which is not less than the predetermined thresholdvalue.

The step S103′ is succeeded by a step S104′ at which the base stationcontrol apparatus 30 determines whether or not the specific base stationis included in the base stations communicating with the mobile station10′. It will be assumed that the specific or the first base station 20′₁is not included in the base stations communicating with the mobilestation 10′. In this event, the step S104′ is followed by a step S105′at which the base station control apparatus 30 instructs the mobilestation 10′ and the specific or the first base station 20′₁ to startcommunication between the mobile station 10′ and the specific or thefirst base station 20′₁.

It will be presumed that the specific or the first base station 20′₁ isincluded in the base stations communicating with the mobile station 10′.Under the circumstances, the step S104′ proceeds to a step S106′ atwhich the base station control apparatus 30 determines whether or notthe base stations communicating with the mobile station 10′ are includedin the specific base station. Inasmuch as the second base station 20′₂is not included in the specific base station, the step S106′ issucceeded by a step S107′ at which the base station control apparatus 30instructs the mobile station 10′ and the second base station 20′₂ tostop communication between the mobile station 10′ and the second basestation 20′₂.

However, it is impossible for this conventional forward transmissionpower control method to secure a user quality in a case where there is alarge fading in a communication channel. This is because thetransmission is always carried out from only one base station on thesoft handover.

In a multimedia communication, prediction is made that a transmissionrate where a large capacity of data is transmitted from a data base at anetwork side to the mobile station is large. When the rate of themultimedia is large in future, it is necessary to increase a radiochannel capacity of the forward link in comparison with that of thereverse link. As a result, it is necessary to decrease the transmissionpower of the forward link.

In addition, as regards the reverse link which is a communicationchannel from the mobile station to the base station, one transmission isalways carried out per communication and an effect of the soft handoveris obtained by receiving in a plurality of base stations. Accordingly,the problem of increasing the transmission power does not arise oncarrying out the soft handover.

At any rate, the above-mentioned conventional CDMA mobile communicationsystem is disadvantageous in that the communication capacity of theforward link is restricted on carrying out the soft handover. This isbecause the transmission power of the forward link per communicationincreases and interference power affecting other communicationsincreases.

Now, the description will be proceed to preferred embodiments of thepresent invention in reference with following figures.

In first through fifth embodiments of the present invention, in a casewhere a soft handover where a plurality of base stations carry outforward transmission of the same contents to one mobile station, when afading in a forward channel is small, communication is carried outbetween the mobile station and the base station having a minimumpropagation loss among the base stations and other base stations turntransmission off.

As regards the mobile station in environment affecting less fading thatis put into, for example, a static state, there is less effect obtainedby transmitting forward transmission signals from the plurality of basestations. Inasmuch as it is possible to minimize a predetermined bitenergy-to-interference ratio Eb/I0 in order to obtaining a predeterminedradio quality under a low-speed fading having a large effect for controlwhich maintains a received power at a constant by a high-speed powercontrol, degradation of a service quality does not occur although theforward transmission is carried out by one base station having theminimum propagation loss.

It is therefore possible to secure a reception character by transmittingthe same signal from a plurality of base stations to the mobile stationwhen a fading in a communication channel with respect to the basestations is large. In addition, it is possible of decrease a forwardchannel capacity due to decrement of interference in the forward linkwith a service quality maintained by transmitting a signal from one basestation to the mobile station when the fading is small.

In addition, the following first through fourth embodiments aredifferent from each other with respect to measurement of magnitude of afading and determination of the base station having a minimumpropagation loss in the manner which will become clear as thedescription proceeds.

Referring to FIGS. 7 through 16, the description will proceed to a CDMAmobile communication system according to a first embodiment of thisinvention. FIG. 7 is a block diagram of the CDMA mobile communicationsystem according to the first embodiment of this invention. Theillustrated CDMA mobile communication system is similar in structure andoperation to the conventional CDMA communication system illustrated inFIG. 1 except that the mobile station, the first and the second basestations are modified from those illustrated in FIG. 1 as will laterbecome clear. The mobile station, the first and the second base stationsare therefore depicted at 10, 20 ₁, and 20 ₂.

FIG. 8 is a block diagram of the mobile station 10 for use in the CDMAmobile communication system illustrated in FIG. 7 while FIG. 9 is ablock diagram of the base station 20 (suffix omitted) for use in theCDMA mobile communication system illustrated in FIG. 7.

As shown in FIG. 8, the illustrated mobile station 10 is similar instructure and operation to the conventional mobile station 10′illustrated in FIG. 2 except that the mobile control section is modifiedfrom that illustrated in FIG. 2 as will later become clear. The mobilecontrol section is therefore depicted at 107.

As shown in FIG. 9, the illustrated base station 20 is similar instructure and operation to the conventional mobile station 20′illustrated in FIG. 3 except that the base control section is modifiedfrom that illustrated in FIG. 3 as will later become clear. The basecontrol section is therefore depicted at 207.

In the first embodiment, the mobile station 10 determines the magnitudeof the fading in the forward link and detects the base station havingthe minimum propagation loss on tie bases of the received power in theperch channel.

Referring to FIG. 10 in addition FIG. 8, description will be made asregards operation of the mobile station 10 in the CDMA mobilecommunication system according the first embodiment.

At a step S101, the mobile control section 107 calculates first throughthird propagation losses in first through third communication channelswhich are established between the mobile station 10 and first throughthird base stations. Specifically, the first through the third perchchannel decoding sections 115 ₁ to 115 ₃ supply the mobile controlsection 107 with first through third transmission power values in firstthrough third perch channels which are sent from the first through thethird base stations carrying out the soft handover. In addition, thefirst through the third perch channel reception level measuring sections106 ₁ to 106 ₃ measures first through third received powers in the firstthrough the third perch channels to produce first through third receivedpower values indicative of the first through the third received powers.The first through the third received power values are supplied to themobile control section 107. The mobile control section 107 calculatesfirst through third differences between the first through the thirdtransmission power values and the first through the third received powervalues. The mobile control section 107 calculates the first through thethird propagation losses in the first though the third communicationchannels on the basis of the first through the third differences.

The step S101 is followed by a step S102 at which the mobile controlsection 107 determines, as a particular base station, one of the firstthrough the third base stations that has a minimum propagation lossamong the first through the third propagation losses.

The step S102 is succeeded by a step S103 at which the mobile controlsection 107 determines whether or not a fading is large by comparing atransmission power control error with a threshold value. Specifically,the mobile reception level measuring section 108 measures the mobilecommunication channel reception level of the mobile synthesized signalto produce the mobile communication channel reception level signalindicative of the measured mobile communication channel reception levelwhich is supplied to the mobile control section 107. The mobile controlsection 107 has a predetermined set reception level so that the forwardreceived user information signal has a predetermined quality. Thepredetermined quality is, for example, that a frame error rate is equalto 0.01. The mobile control section 107 determines, as the transmissionpower control error, a difference between the measured mobilecommunication channel reception level and the predetermined setreception level.

Turning to FIGS. 11A, 11B, 11C, 12A, 12B, and 12C, the description willproceed to a concrete method which carries out determination of largeand small in the fading. FIGS. 11A through 11C collectively showvariation of the measured mobile communication channel reception levelunder the transmission power control when the fading is large. FIG. 11Ashows variation of the measured mobile communication channel receptionlevel in a case where the transmission power control is not carried out.FIG. 11B shows variation of the transmission power under thetransmission power control. FIG. 11C shows variation of the measuredmobile communication channel reception level in a case where thetransmission power control is carried out.

Likewise, FIGS. 12A through 12C collectively show variation of themeasured mobile communication channel reception level under thetransmission power control when the fading is small. FIG. 12A showsvariation of the measured mobile communication channel reception levelin a case where the transmission power control is not carried out. FIG.12B shows variation of the transmission power under the transmissionpower control. FIG. 12C shows variation of the measured mobilecommunication channel reception level in a case where the transmissionpower control is carried out.

Detection of a fading amount in a communication channel is achieved bymeasuring a variation amount in the reception level on the transmissionpower control or the transmission power control error which is an errorbetween a target received power and an actually received power and bycalculating variance or standard deviation of the variation amount inthe reception level or the transmission power control error.

It will be assumed that the variation of the fading in the communicationchannel is gentle as shown in FIGS. 12A through 12C. In this event, thevariation amount in the reception level or the transmission powercontrol error is small. This is because it is possible to maintain thereceived power at a constant due to a high-speed power control. It willbe assumed that the variation of the fading in the communication channelis violent as shown in FIGS. 11A through 11C. In this event, thevariation amount in the reception level or the transmission powercontrol error is large. This is because it is difficult to accuratelymaintain the received power at the constant due to the high-speed powercontrol.

In addition, the variation amount in the reception level or thetransmission power control error may be calculated by averaging thereception level every predetermined period, using a method of movingaverages, or using an oblivion coefficient.

Turning to FIG. 13, the description will proceed to the method of movingaverages. The method of moving averages is a method of successivelycalculating averages of a plurality of values at time instants for apredetermined time interval. It will be assumed that values a, a₂, a₃,a₄, a₅, a₆, a₇, a₈, a₉, . . . , and so on are obtained as illustrated inFIG. 11. In this event, values by means of the moving averages are anaverage value of the values a₁ to a₅ at a time instant when the value a₅is obtained, an average value of the values a₂ to a₆ at a time instantwhen the value a₆ is obtained, an average value of the values a₃ to a₇at a time instant when the value a₇ is obtained, and so on.

Turning to FIG. 14, the description will proceed to the method of usingthe oblivion coefficient. The method of using the oblivion coefficientis a method of calculating a current value by adding a value obtained bymultiplying a preceding value before a time instant by the oblivioncoefficient less than one to another value obtained by multiplying avalue at the time instant by a value which is obtained by subtractingthe oblivion coefficient from one. FIG. 14 is a block diagram showingcalculation of the method of using the oblivion coefficient.

As illustrated in FIG. 14, a calculating circuit comprises first andsecond multipliers 61 and 62, and an adder 63. In FIG. 14, the oblivioncoefficient is depicted at β. The first multiplier 61 is given by theoblivion coefficient β while the second multiplier 62 is given by thevalue (1−β) obtained by subtracting the oblivion coefficient β from one.The first multiplier 61 is supplied with a preceding output value whilethe second multiplier 62 is supplied with a current input value. Thefirst multiplier 61 multiplies the preceding output value by theoblivion coefficient β to produce a first multiplied value. The firstmultiplied value is supplied to the adder 63. The second multiplier 62multiplies the current input value by the value (1−β) to produce asecond multiplied value. The second multiplied value is supplied to theadder 63. The adder 63 adds the first multiplied value and the secondmultiplied value to produce an added value as a current output value.

In addition, another method of detecting the magnitude of the fading isa method of measuring variance or standard deviation of variation amountin a fading vector which is obtained by carrying out channel estimation.The mobile control section 107 determines that the fading is large whenthe variance or the standard deviation of the variation amount in thefading vector is larger than the threshold value. On the other hand, themobile control section 107 determines that the fading is small when thevariance or the standard deviation of the variation amount in the fadingvector is smaller than the threshold value. The variance or the standarddeviation of the variation amount in the fading vector is alsocalculated by averaging the fading vector every predetermined period,using the method of moving averages, or using the oblivion coefficient.

Turning back to FIG. 10, the step S103 proceeds to a step S104 at whichthe mobile control section 107 sets a forward transmission powerinformation signal including the fading information signal and theminimum propagation loss base station information signal instead of themobile transmission user data signal in the mobile encoding section 112periodically, or when the base station having the minimum propagationloss is changed, or the determined result of the magnitude of the fadingis changed. In addition, the mobile control section 107 sets, as anerror detection information signal for carrying out error detection inthe forward transmission power information signal, a cyclic redundancycheck (CRC) information signal in the mobile encoding section 112.

FIGS. 15A and 15B show signal formats for the forward link and thereverse link, respectively. As shown in FIG. 15A, the base station 20transmits a reverse transmission power control information signalincluding a pilot information signal, a transmission power control (TRC)information signal, and a user information signal to the mobile station10 via the forward link. As shown in FIG. 15B, the mobile station 10transmits the forward transmission power control information signalincluding a pilot information signal, a TRC information signal, thefading information signal, the minimum propagation loss base stationinformation signal, and the CRC information signal to the base station20 via the reverse link.

Referring to FIG. 16 in addition to FIG. 9, the description will proceedto operation of the base station 20 in the CDMA mobile communicationsystem.

At a step S201, the base decoding section 204 decodes the informationsignal transmitted from the reverse link into a decoded informationsignal. The decoded information signal is supplied to the base controlsection 207. When the decoded information signal is the forwardtransmission power control information signal as shown in FIG. 15B, thebase decoding section 204 carries out, using the CRC information signal,an error detection on the fading information signal and the minimumpropagation loss base station information signal. An detected result issupplied from the base decoding section 204 to the base control section207. The step S201 is followed by a step S202 at which the base controlsection 207 determines whether or not any error is detected on thereverse link on the basis of the detected result. When any error is notdetected in the fading information signal and the minimum propagationloss base station by the error detection, the step S202 proceeds to astep S203 at which the base control section 207 determines whether ornot the fading indicated by the fading information signal has amagnitude value which is smaller than a predetermined threshold value.When the magnitude value of the fading information signal is smallerthan the predetermined threshold value, the step S203 is succeeded by astep S204 at which the base control section 207 determines whether ornot its own base station 20 corresponds to the minimum propagation lossbase station indicated by the minimum propagation loss base stationinformation signal. When its own base station 20 does not correspond tothe minimum propagation loss base station, the step S204 is followed bya step S205 at which the base station section 207 supplies the basetransmission power calculating section 211 with the forward transmissionon/off instruction signal indicative of turning the forward transmissionoff. Accordingly, the base station 20 transmits the forward transmissionsignal.

Otherwise, the steps S202, S203, and S204 proceed to a step S206 atwhich the base control section 207 supplies the base transmission powercalculating section 211 with the forward transmission on/off instructionsignal indicative of turning the forward transmission on. Specifically,the base control section 207 supplies the base transmission powercalculating section 211 with the forward transmission on/off instructionsignal indicative of turning the forward transmission on when any erroris detected in the fading information signal and the minimum propagationloss base station by the error detection, when the magnitude value ofthe fading is not smaller than the predetermined threshold value, orwhen its own base station 20 corresponds to the minimum propagation lossbase station. In this event, the base station 20 transmits the forwardtransmission signal.

The forward transmission power control method according to the firstembodiment of this invention is reliable because the transmission powercontrol for the forward link is carried out by using the informationsignal indicative of condition of the forward link. However, it isnecessary to transmit the forward transmission power information signalfrom the mobile station 10 to the base station 20 via the reverse link.Accordingly, the format for transmitting the fading information signaland the minimum propagation loss base station information signal as theforward transmission power information signal must coincide with astandardized format.

Referring to FIGS. 17 through 21, the description will proceed to a CDMAmobile communication system according to a second embodiment of thisinvention. FIG. 17 is a block diagram of the CDMA mobile communicationsystem according to the second embodiment of this invention. Theillustrated CDMA mobile communication system is similar in structure andoperation to the conventional CDMA communication system illustrated inFIG. 1 except that the mobile station, the first and the second basestations, and the base station control apparatus are modified from thoseillustrated in FIG. 1 as will later become clear. The mobile station,the first and the second base stations, and the base station controlapparatus are therefore depicted at 10A, 20A₁, 20A₂, and 30A.

FIG. 18 is a block diagram of the mobile station 10A for use in the CDMAmobile communication system illustrated,in FIG. 17 while FIG. 19 is ablock diagram of the base station 20A (suffix omitted) for use in theCDMA mobile communication system illustrated in FIG. 17.

As shown in FIG. 18, the illustrated mobile station 10A is similar instructure and operation to the conventional mobile station 10′illustrated in FIG. 2 except that the mobile control section is modifiedfrom that illustrated in FIG. 2 as will later become clear. The mobilecontrol section is therefore depicted at 107A.

As shown in FIG. 19, the illustrated base station 20A is similar instructure and operation to the conventional mobile station 20′illustrated in FIG. 3 except that the base control section is modifiedfrom that illustrated in FIG. 3 as will later become clear. The basecontrol section is therefore depicted at 207A.

As shown in FIG. 17, the illustrated base station control apparatus 30Ais similar in structure and operation to the base station controlapparatus 30 illustrated in FIG. 1 except that the control section ismodified from that illustrated in FIG. 1 as will later become clear. Thecontrol section is therefore depicted at 32A.

In the second embodiment, a combination of the base stations 20A₁, 20A₂and the base station control apparatus 30A determines the magnitude ofthe fading in the reverse link and the mobile station 10A detects thebase station having the minimum propagation loss on the bases of thereceived power in the perch channel.

Referring to FIG. 20 in addition to FIG. 18, description will be made asregards operation of the mobile station 10A in the CDMA mobilecommunication system according to the second embodiment of thisinvention.

The mobile station 10A is similar in operation to the mobile station 10illustrated in FIG. 10 except that the step S103 is omitted therefromand another step S105 is added in lieu of the step S104.

Periodically or when the minimum propagation loss base station ischanged, the step S102 is followed by the step S105 at which the mobilecontrol section 107A sets a forward transmission power informationsignal including the minimum propagation loss base station informationsignal instead of the mobile transmission user data signal in the mobileencoding section 112. In addition, the mobile control section 107A sets,as an error detection information signal for carrying out errordetection in the forward transmission power information signal, a cyclicredundancy check (CRC) information signal in the mobile encoding section112.

Referring to FIG. 21 in addition to FIGS. 17 and 19, description will bemade as regards operations of the first and the second base stations20A1 and 20A2 and the base station control apparatus 30A in the CDMAmobile communication system according to the second embodiment of thisinvention.

Each of the first and the second base stations 20A₁ and 20A₂ is similarin operation to the base station 20 illustrated in FIG. 16 except that anew step S207 is inserted between the steps S201 and S202.

At the step S207, the base control section 207A in each of the first andthe second base stations 20A₁ and 20A₂ carries out a large or smalldecision of a fading by measuring whether or not a transmission powercontrol error in the reverse link is not less than a predeterminedthreshold value. The base control section 207A sends a decided result ofthe fading as the control information signal 52 to a control section 32Aof the base station control apparatus 30A.

Specifically, the base control section 207A in the first base station20A₁ sends a first decided result of the fading to the control section32A of the base station control apparatus 30A while the base controlsection 207A in the second base station 20A₂ sends a second decidedresult of the fading to the control section 32A of the base stationcontrol apparatus 30A. When any one of the first and the second decidedresults of the fading indicates that the fading is large, the controlsection 32A of the base station control apparatus 30A sends its effectto the first and the second base stations 20A₁ and 20A₂. When all of thefirst and the second decided results of the fading indicate the fadingis small, the control section 32A of the base station control apparatus30A sends its effect to the first and the second base stations 20A₁ and20A₂.

The forward transmission power control method according to the secondembodiment of this invention is reliable because the transmission powercontrol for the forward link is carried out by using the informationsignal indicative of condition of the forward link. However, it isnecessary to transmit the forward transmission power information signalfrom the mobile station 10A to the base station 20A via the reverselink. Accordingly, the format for transmitting the minimum propagationloss base station information signal as the forward transmission powerinformation signal must coincide with a standardized format. Inaddition, an error caused by a difference between a reverse linkfrequency and a forward link frequency may be included in the fadinginformation signal because the fading information signal is obtainedfrom propagation conditions in the reverse links.

In the second embodiment, each base station sends the large or smalldecided result of the fading to the base station control apparatus andto turn the forward transmission off may be allowed each base station ina case where its own base station corresponds to the minimum propagationloss base station only when the base station control apparatusdetermines that the fading is small in all base stations. However, eachbase station may determine by itself without sending of the large orsmall decided result of the fading to the base station control apparatusand may turn the forward transmission off when the fading is small andwhen its own base station does not correspond to the minimum propagationloss base station. In this event, it is possible to rapidly carry outthe transmission power control. This is because it is unnecessary tocarry out exchange of the control information signal between each basestation and the base station control apparatus.

Referring to FIGS. 22 through 26, the description will proceed to a CDMAmobile communication system according to a third embodiment of thisinvention. FIG. 22 is a block diagram of the CDMA mobile communicationsystem according to the third embodiment of this invention. Theillustrated CDMA mobile communication system is similar in structure andoperation to the conventional CDMA communication system illustrated inFIG. 1 except that the mobile station, the first and the second basestations, and the base station control apparatus are modified from thoseillustrated in FIG. 1 as will later become clear. The mobile station,the first and the second base stations, and the base station controlapparatus are therefore depicted at 10B, 20B₁, 20B₂, and 30B.

FIG. 23 is a block diagram of the mobile station 10B for use in the CDMAmobile communication system illustrated in FIG. 22 while FIG. 24 is ablock diagram of the base station 20B (suffix omitted) for use in theCDMA mobile communication system illustrated in FIG. 22.

As shown in FIG. 23, the illustrated mobile station 10B is similar instructure and operation to the conventional mobile station 10illustrated in FIG. 2 except that the mobile control section is modifiedfrom that illustrated in FIG. 2 as will later become clear. The mobilecontrol section is therefore depicted at 107B.

As shown in FIG. 24, the illustrated base station 20B is similar instructure and operation to the conventional mobile station 20′illustrated in FIG. 3 except that the base control section is modifiedfrom that illustrated in FIG. 3 as will later become clear. The basecontrol section is therefore depicted at 207B.

As shown in FIG. 22, the illustrated base station control apparatus 30Bis similar in structure and operation to the base station controlapparatus 30 illustrated in FIG. 1 except that the control section ismodified from that illustrated in FIG. 1 as will later become clear. Thecontrol section is therefore depicted at 32B.

In the third embodiment, the mobile station 10B determines the magnitudeof the fading in the forward link and a combination of the base stations20B₁, 20B₂ and the base station control apparatus 30B determines thebase station having the minimum propagation loss on the bases of thereceived power in the perch channel.

Referring to FIG. 25 in addition to FIG. 23, description will be made asregards operation of the mobile station 10B in the CDMA mobilecommunication system according to the third embodiment of thisinvention.

The mobile station 10B is similar in operation to the mobile station 10illustrated in FIG. 10 except that the steps S101 and S102 are omittedtherefrom and another step S106 is added on behalf of the step S104.

Periodically or when the decided result of the magnitude of the fadingis changed, the step S103 is followed by the step S106 at which themobile control section 107B sets a forward transmission powerinformation signal including the fading information signal instead ofthe mobile transmission user data signal in the mobile encoding section112. In addition, the mobile control section 107B sets, as an errordetection information signal for carrying out error detection in theforward transmission power information signal, a cyclic redundancy check(CRC) information signal in the mobile encoding section 112.

Referring to FIG. 26 in addition to FIGS. 22 and 24, description will bemade as regards operations of the first and the second base stations20B₁ and 20B₂ and the base station control apparatus 30B in the CDMAmobile communication system according to the third embodiment of thisinvention.

Each of the first and the second base stations 20B₁ and 20B₂ is similarin operation to the base station 20 illustrated in FIG. 16 except that anew step S208 is inserted between the steps S201 and S202.

At the step S208, the base control section 207B in each of the first andthe second base stations 20B₁ and 20B₂ measures a received bitenergy-to-interference ratio, Eb/I0, in a communication channel. Thebase control section 207B sends a received bit energy-to-interferenceratio signal indicative of the received bit energy-to-interference ratioEb/I0 as the control information signal 52 to the control section 32B ofthe base station control apparatus 30B.

Specifically, the base control section 207B in the first base station20B₁ sends, to the control section 32B of the base station controlapparatus 30B, a first received bit energy-to-interference ratio signalindicative of a first received bit energy-to-interference ratio Eb/I0 ina first communication channel between the mobile station 10B and thefirst base station 20B₁. In addition, the base control section 207B inthe second base station 20B₂ sends, to the control section 32B of thebase station control apparatus 30B, a second received bitenergy-to-interference ratio signal indicative of a, second received bitenergy-to-interference ratio Eb/I0 in a second communication channelbetween the mobile station 10B and the first base station 20B₂. Thecontrol section 32B of the base station control apparatus 30Bdetermines, as the minimum propagation loss base station, one of thefirst and the second base stations 20B₁ and 20B₂ that has a maximumreceived bit energy-to-interference ratio by comparing the first and thesecond received bit energy-to-interference ratios Eb/I0. The controlsection 32B of the base station control apparatus 30B sends itsdetermined result as the minimum propagation loss base stationinformation signal to the first and the second base stations 20B₁ and20B₂.

The forward transmission power control method according to the thirdembodiment of this invention is reliable because the transmission powercontrol for the forward link is carried out by using the informationsignal indicative of a condition of the forward link. However, it isnecessary to transmit the forward transmission power information signalfrom the mobile station 10B to the base station 20B via the reverselink. Accordingly, the format for transmitting the fading informationsignal as the forward transmission power information signal mustcoincide with a standardized format. In addition, an error caused by adifference between a reverse link frequency and a forward link frequencymay be included in the fading information signal because the minimumpropagation loss base station information signal is obtained frompropagation conditions in the reverse links. Furthermore, a controldelay occurs. This is because information signals related to thepropagation losses in the communication channels obtained by the basestations are collected in the base station control apparatus, the basestation control apparatus determines the minimum propagation loss basestation and sends the minimum propagation loss base station informationsignal to each base station.

Referring to FIGS. 27 through 29, the description will proceed to a CDMAmobile communication system according to a fourth embodiment of thisinvention. FIG. 27 is a block diagram of the CDMA mobile communicationsystem according to the fourth embodiment of this invention. Theillustrated CDMA mobile communication system is similar in structure andoperation to the conventional CDMA communication system illustrated inFIG. 1 except that the first and the second base stations and the basestation control apparatus are modified from those illustrated in FIG. 1as will later become clear. The first and the second base stations andthe base station control apparatus are therefore depicted at 20C₁, 20C₂,and 30C.

FIG. 28 is a block diagram of the base station 20C (suffix omitted) foruse in the CDMA mobile communication system illustrated in FIG. 27.

As shown in FIG. 28, the illustrated base station 20C is similar instructure and operation to the conventional mobile station 20′illustrated in FIG. 3 except that the base control section is modifiedfrom that illustrated in FIG. 3 as will later become clear. The basecontrol section is therefore depicted at 207C.

As shown in FIG. 27, the illustrated base station control apparatus 30Cis similar in structure and operation to the base station controlapparatus 30 illustrated in FIG. 1 except that the control section ismodified from that illustrated in FIG. 1 as will later become clear. Thecontrol section is therefore depicted at 32C.

In the fourth embodiment, a combination of the base stations 20C₁, 20C₂and the base station control apparatus 30C determines the magnitude ofthe fading in the reverse link and determines the base station havingthe minimum propagation loss on the bases of the received power in thereverse link.

Referring to FIG. 29 in addition to FIGS. 27 and 28, description will bemade as regards operations of the first and the second base stations20C₁ and 20C₂ and the base station control apparatus 30C in the CDMAmobile communication system according to the fourth embodiment of thisinvention.

Each of the first and the second base stations 20C₁ and 20C₂ is similarin operation to the base station 20 illustrated in FIG. 16 except thatthe steps S201 and S202 are omitted and the steps S207 and S208 areadded.

Inasmuch as the steps S207 and S208 are already described above,description thereof is omitted for the purpose of simplification ofdescription.

In the fourth embodiment, it is unnecessary to change a normal format.This is because it is unnecessary to transmit the forward transmissionpower information signal from the mobile station 10′ to the base station20C. In addition, an error caused by a difference between a reverse linkfrequency and a forward link frequency may be included in the minimumpropagation loss base station information signal and the fadinginformation signal because the minimum propagation loss base stationinformation signal and the fading information signal are obtained frompropagation conditions in the reverse links. Furthermore, a controldelay occurs. This is because information signals obtained by the basestations are collected in the base station control apparatus, the basestation control apparatus determines the minimum propagation loss basestation and a large or small of the fading, and sends the minimumpropagation loss base station information signal and the fadinginformation signal to each base station.

In the fourth embodiment, each base station sends the large or smalldecided result of the fading to the base station control apparatus andto turn the forward transmission off may be allowed each base station ina case where its own base station corresponds to the minimum propagationloss base station only when the base station control apparatusdetermines that the fading is small in all base stations. However, eachbase station may determine by itself without sending of the large orsmall decided result of the fading to the base station control apparatusand may turn the forward transmission off when the fading is small andwhen its own base station does not correspond to the minimum propagationloss base station. In this event, it is possible to rapidly carry outthe transmission power control. This is because it is unnecessary tocarry out exchange of the control information signal between each basestation and the base station control apparatus.

Referring to FIG. 30, the description will proceed to a CDMA mobilecommunication system according to a fifth embodiment of this invention.In the CDMA mobile communication system, at least two of theabove-mentioned first through fourth embodiments of this invention iscombined with one another. Although the above-mentioned first throughfourth embodiments of this invention may be operable in each otherindependently, it is possible for the fifth embodiment of this inventionto make variance of a system large by combining the at least two of theabove-mentioned first through fourth embodiments of this invention.

FIG. 30 shows differences among the CDMA mobile communication systemsaccording to the first through the fourth embodiments of this invention.

It will be assumed that the first and the fourth embodiments of thisinvention are combined with each other. Under the circumstances, themobile station determines the magnitude of the fading on the forwardlink and determines the minimum propagation loss base station on thebasis of the received power on the perch channels. In addition, acombination of the base station and the base station control apparatusdetermines a large or small magnitude of the fading on the reverse linkand determines the minimum propagation loss base station on the basis ofthe received power on the reverse link. In addition, the combination ofthe base station and the base station control apparatus carries outon-off control of the forward transmission in the base station on thebasis of a plurality of information signals indicative of the magnitudeof the fading and of the minimum propagation loss base station.

In this event, it may be possible to use, for instance, three controlmethods in the manner which will presently be described.

(1) Inasmuch as the base station cannot use the forward transmissionpower information signal on the reverse link when an error is detectedon the reverse link, the base station carries out on-off control of theforward transmission therein using a large or small information signalof the fading and a transmission on-off information signal which areobtained by the combination of the base station and the base stationcontrol apparatus.

(2) The base station turns the forward transmission off when both adecided result on the basis of information obtained by the reverse linkand a decided result on the basis of information obtained by thecombination of the base station and the base station control apparatusindicate turning the forward transmission off.

(3) The base station turns the forward transmission off when either adecided result on the basis of information obtained by the reverse linkor a decided result on the basis of information obtained by thecombination of the base station and the base station control apparatusindicates turning the forward transmission off.

Although a method of carrying out the forward transmission power controlby combining a plurality of information signals such as the fifthembodiment of this invention is disadvantageous in that it iscomplicated in structure, this method is advantageous in that it ispossible to improve reliability in transmission switching control.

Referring to FIG. 31, the description will proceed to a CDMA mobilecommunication system according to a sixth embodiment of this invention.

In the CDMA mobile communication system, although one base stationcovers one cell, sectorization of the cell is carried out in order tomake capacity of a communication channel larger. The “sectorization” isa method of dividing the cell into a plurality of (e.g. three, six, orthe like) areas by making an antenna of the base station havedirectivity. In addition, the area obtained by dividing the cell iscalled a sector.

FIG. 31 shows the CDMA mobile communication system where thesectorization is carried out. In FIG. 31, the illustrated CDMA mobilecommunication system comprises first through third base stations 20 ₁,20 ₂, and 20 ₃ which cover first through third cells 71, 72, and 73,respectively. In addition, the first cell 71 is divided into threesectors 71 a, 71 b, and 71 c as shown in FIG. 31. Likewise, each of thesecond and the third cells 72 and 73 is divided into three sectors, asshown in FIG. 31.

In the manner known in the art, the soft handover, which is carried outwhen the mobile station 10 moves between different sectors, is referredto as a softer handover.

It will be assumed that the mobile station 10 lies in an area in whichthe first through the third cells 71 to 73 are overlapped in such asectorized CDMA mobile communication system as illustrated in FIG. 31.In this event, the mobile station 10 may be assigned with eight forwardchannels when the soft or the softer handover is carried out.

It will be presumed that the forward transmission power control methodsaccording to the above-mentioned first through fifth embodiments areapplied to the sectorized CDMA mobile communication system. In aconventional forward transmission power control method, other sevenchannels other than one channel are put into a transmission off statewhen the soft or the softer handover is carried out using the eightforward channels. However, a difference is too large between that thehandover is carried out using the eight forward channel and that onlyone forward channel is used. Accordingly, a case where degradation of aservice quality cannot be accepted may occurs although the fading issmall.

In order to resolve the above-mentioned problem, the forwardtransmission power control method according to the sixth embodiment ofthis invention controls so that all of the base stations, each of whichhas the propagation loss in the communication channel not more than apredetermined value, turn the forward transmission on without turningthe forward transmission in only one base station having a minimumpropagation loss on. In addition, the forward transmission power controlmethod according to the sixth embodiment of this invention controls sothat only the base station having the minimum propagation loss turns theforward transmission on when all base stations have the propagationlosses which are more than the predetermined value.

By carrying out such a control, at least one base station turns theforward transmission on and a plurality of base stations having a smallpropagation loss normally turn the forward transmission on. As a result,it is possible for the sixth embodiment of this invention to restrainthe degradation of the service quality to the minimum.

In the CDMA mobile communication systems according to theabove-mentioned first through sixth embodiments of this invention,on-off control of the forward transmission power may be carried outevery frame or may be carried out every slot.

While this invention has thus far been described in conjunction with afew preferred embodiments thereof, it will now be readily possible forthose skilled in the art to put this invention into various othermanners. For example, by using the received power level in lieu of thepropagation loss, a determination of the base station may be carried outwhich has the best channel for the mobile station although each of theabove-mentioned first through sixth embodiments of this inventiondetermines the propagation losses of the communication channels andcarries out the forward transmission power control so that the channelbetween the mobile station and the base station having the minimumpropagation loss is the best channel. In this event, of course, thedetermination is made so that the base station having a maximum receivedpower level is the base station having the best channel.

Furthermore, in the above-mentioned first through sixth embodiments ofthis invention, on carrying out the soft handover or the softerhandover, the communication capacity of the forward channel is decreasedso that only the base station having the minimum propagation loss in thecommunication channel for the mobile station communicates with themobile station as the minimum propagation loss base station and otherbase stations turn the forward transmission off. However, this inventionis not restricted to such a control. For example, it is possible todecrease the communication capacity of the forward channel by carryingout control so as to lower the transmission power in the forwardtransmission from an original value without perfectly turning theforward transmission off in the other base stations except for theminimum propagation loss base station.

1. A method of controlling communication in a code division multipleaccess (CDMA) mobile communication system, in which a mobile stationperforms soft handover with plural base stations, comprising: monitoringreception quality of signals, in said mobile station, from the pluralbase stations that are in the soft handover state; comparing saidreception quality of signals from respective base stations in saidmobile station; determining a specific base station based on a result ofsaid monitoring reception quality in said mobile station; transmittinginformation about said specific base station from said mobile station tosaid plural base stations; receiving the information about said specificbase station in said plural base stations; and determining, in each ofsaid plural base stations, whether to turn off a forward transmissionbased on said information about said specific base station and amagnitude of fading in communication channels between said mobilestation and each of plural base stations.
 2. The method as claimed inclaim 1, wherein each of said base stations turns off said forwardtransmission if said magnitude of said fading is smaller than apredetermined value.
 3. A code division multiple access (CDMA) mobilecommunication systems in which a mobile station performs soft handoverwith plural base stations, said mobile station comprising: monitoringmeans for monitoring reception quality of signals from the plural basestations that are in the soft handover state; base station specifyingmeans for determining a specific base station based on said receptionquality; and transmitting means for transmitting information about saidspecific base station to said plural base stations; said base stationseach comprising: receiving means for receiving the information aboutsaid specific base station; and transmission control means fordetermining whether to turn off a forward transmission based on saidinformation about said specific base station and a magnitude of fadingin communication channels between said mobile station and each of saidplural base stations.
 4. The system as claimed in claim 3, wherein saidtransmission control means turns off said forward transmission if saidmagnitude of said fading is smaller than a predetermined value.
 5. Amobile station for a code division multiple access (CDMA) mobilecommunication system, in which said mobile station performs softhandover with plural base stations, said mobile station comprising:monitoring means for monitoring reception quality of signals from theplural base stations that are in the soft handover state; base stationspecifying means for determining a specific base station based on saidreception quality; and transmitting means for transmitting informationabout said specific base station to said plural base stations andinformation about a magnitude of fading in communication channelsbetween said mobile station and said plural base stations, wherein saidspecific base station determines whether to turn off a forwardtransmission based on said information about said specific base stationand a magnitude of fading in communication channels between said mobilestation and each of said plural base stations.
 6. A base station for acode division multiple access (CDMA) mobile communication system, inwhich a mobile station performs soft handover with plural base stations,said base station comprising: receiving means for receiving from saidmobile station information about specific base station specified basedon reception quality at said mobile station; and transmission controlmeans for determining whether to turn off a forward transmission basedon said information about said specific base station and a magnitude offading in communication channel between said mobile station and saidbase station.